People lay flowers at a memorial to Armenians killed by the Ottoman Turks as they mark the centenary of the killings in Yerevan, Armenia, on April 24. Armenians on Friday marked the centenary of what historians estimate to be the slaughter of as  many as 1.5 million Armenians by Ottoman Turks, an event widely viewed by scholars as genocide. Turkey, however, denies that the deaths constituted genocide and says the death toll has been inflated. (Sergei Grits/AP)

This week is being marked as the 100th anniversary of the killings of more than a million Armenians during the dying days of the Ottoman Empire. Despite considerable opposition from the Turkish government, the anniversary is bringing renewed attention to an often overlooked historical issue, with President Obama in particular facing criticism for not using the word "genocide" to describe the killings.

This didn't happen by accident. The attention placed on the massacre this year is the result of a long and coordinated campaign by Armenia and the Armenian diaspora to ensure that a dark and sometimes disputed part of history wasn't forgotten. It was this campaign that has slowly dragged the Armenian tragedy out of obscure disputes and into mainstream discussion.

It doesn't always work that way, though. In fact, what happens far more often is that the difficult parts of history often are forgotten or ignored. The 20th century was bloody and violent, and while some horrors are at least relatively well-known – the Holocaust or the genocides in Rwanda and Cambodia, for example – others have become mere footnotes in history.

So, in honor of the 100th anniversary of the Armenian killings, here are some of the lesser-known massacres of the 20th century, many of which are considered genocides, too.

Unfortunately, because history is so bloody, this list is far from exhaustive.

The Herero and Namaqua genocide


Reporting of the revolt against the German colonizers in a U.S. newspaper, the Tacoma Times, on March 2, 1904. (Wikimedia Commons)

When Pope Francis referred to the 1915 killings recently and sparked a backlash from Turkey, he not only called the killings a genocide, but also "the first genocide of the 20th century." Even if historians would agree with the former, they might have some disagreements with the latter.

Between 1904 and 1908, tens of thousands of Herero and Namaqua people were killed in what is now Namibia during German colonial rule. These people were indigenous to an area then known a German South West Africa which was the first colony of Germany, a latecomer to the imperial land grab. After uprisings by both the Herero and the Namaqua, a German general in charge of the region ordered that the indigenous  people should be "annihilated" or, if this was not possible, expelled from the land.

Unarmed men, women and children were killed by German troops, and huge numbers of Herero and Namaqua people were sent to concentration camps as a form of collective punishment. It's now thought that as many as 70,000 Herero and 7,000 Namaqua died.

In 2004, Germany apologized for the killings, now thought to be the first genocide of the 20th century. Many see the killings as a precursor to the Holocaust.

The Ottoman killings of Assyrians and Greeks


Christian children lie on the floor with mock blood as Saint Georges Assyrian Church holds a public demonstration commemorating Assyrian Martyr Day on Aug. 7, 2014, in Beirut's Fanar district. It honored "the 2,000 years of massacres" suffered by the Assyrians, from 330 AD to 2014, making particular reference to killings under the Ottoman Empire in 1915 and the current expulsion of Christians from Iraq under Sunni jihadists from the Islamic State. According to Saint George Assyrian Church officials, in Lebanon there are 7,000 Lebanese Assyrians, 7,000 Syrian Assyrians, and about 200 from Iraq. The influx of Iraqi Assyrians is rising since Islamic State persecution.  (Maya Hautefeuille/AFP/Getty Images)

The Armenians weren't the only group targeted during the chaotic collapse of the Ottoman Empire.

It's thought that as many as 250,000 Assyrians, mostly Christians, living in Mesopotamia were killed by Ottoman forces during the period around World War I. Many of those who survived were dispersed throughout the Middle East. A handful of governments, including Armenia, have recognized the killings as a genocide.

At the same time, in Anatolia, the Ottoman Empire killed hundreds of thousands of Greek Christians. While the total number of deaths is unclear, some estimates put it at more than 1 million. Since 1994, Greece has held a remembrance for the killings, which it views as a genocide.

Holodomor


A woman leaves a candle in memory of the victims of the Holodomor famine during a ceremony at the Holodomor memorial in Kiev on Nov. 24, 2012.  (Sergei Supinsky/AFP)

Between 1932 and 1933, estimates say that as many of 10 million Ukrainians – almost a third of the population at the time – were killed by a devastating famine. The mass starvation was of a truly horrific scale: There were reports of cannibalism, and entire villages were wiped out.

It's not just the scale of the famine that merits its inclusion here. Most agree now that the famine was man-made, designed by Soviet leader Joseph Stalin to either eradicate private landowners or perhaps the targeting of Ukrainians as an ethnic group.

In 2006, Ukraine's parliament officially recognized the "Holodomor" – or "Death by Hunger" – as a genocide. But Russia, like the Soviet Union before it, has resisted calls for any compensation for the mass deaths.

The Nanking Massacre


The destruction of Nanking, known as the rape of Nanking, following its capture by the Japanese Imperial Army during its invasion of China during the second Sino-Japanese War on Dec. 29, 1937. (AP)

In 1937, during the Sino-Japanese war, the Imperial Japanese Army marched into Nanking, then the Chinese capital. The city, now known as Nanjing, was left virtually undefended, and tens of thousands of civilians were killed, if not more (Chinese historians tend to put the number at 300,000, a higher estimate than their Western peers).

The six-week spree of violence left the city devastated in many ways. The post-World War II International Military Tribunal for the Far East concluded that some 20,000 rapes occurred during the first month of Japanese occupation, lending the tragedy its other grim name: "The Rape of Nanking."

Thanks to some remarkable scholarship over the past few decades, the Nanking Massacre is hardly obscure anymore. But it remains a disputed issue, with Japanese nationalists (and the current Japanese government) accused of downplaying its significance, or even suggesting that it never happened.

The German Expulsions


Former camp for expellees in Eckernförde, Germany, in 1951 (Bundesarchiv)

While the horrors committed by Nazi Germany are well known, what's lesser acknowledged is what happened to the Germans scattered in Eastern Europe after Germany lost the war.

These Germans, who had been left living in places that reverted to Poland, Czechoslovakia and the Soviet Union, had to make their way back to Germany and Austria. Many were forcibly expelled from their homes, some were sent to internment camps.

R.M. Douglas, a historian who studies the expulsions, has described it as "not merely the largest forced migration but probably the largest single movement of population in human history," with more than 12 million civilians forced out. It was effectively what would now be considered "ethnic cleansing," Douglas argued, and, inevitably, masses died – at least 473,000 by one count.

"The Nazis' crimes had been far worse," German newspaper Der Spiegel wrote in 2011, "but the suffering of ethnic Germans was immense."

The aftermath of the 30th September Movement

In his genre-bending documentary, "The Act of Killing," director Joshua Oppenheimer invites a group of former Indonesian death-squad leaders to reenact the real life executions they performed in the 1960s. (Lee Powell/The Washington Post)

Following a failed coup d'etat in 1965 by a group referred to as the 30th September Movement, General Suharto led an anti-communist purge in Indonesia that eventually turned into widespread massacres around the country. In the end, the Indonesian Communist Party (PKI), once one of the largest, was virtually wiped out: Estimates for the number of dead start at 500,000.

For decades, there was little discussion of the killings in 1965-1966. Few foreign observers saw the events and many foreign governments – including the United States – viewed the anti-communist movement as a good thing. When Suharto became president in 1967, an official silence was installed across the country. Suharto would end up being president for 32 years: To this day, communist organizations are officially banned.

It was only in the past few years that discussions about the terrible events began to take place. In 2010, Indonesia's Constitutional Court struck down a ban on several books about the coup that mentioned the killings. In 2012, American filmmaker Joshua Oppenheimer released "The Act of Killing," a documentary that saw perpetrators act out their killings, which sparked renewed international attention.

The Bangladesh Genocide

The Partition of India after 1947 saw one of the world's largest migrations ever: Some estimates suggest 2 million or more died in the chaos. It also left Pakistan split between the main rump of its body to the west of the new state of India, and a smaller province of East Bengal, later renamed East Pakistan, to the east.

This split state didn't last, with terrible consequences. In 1971, West Pakistan began a military crackdown on Bengali calls for independence, which eventually led to a nine-month war that birthed Bangladesh.

That war resulted in an estimated 10 million refugees, and while there is no clear death toll, estimates put the number of deaths in the tens, if not hundreds, of thousands. The Bangladeshi government has said that as many as 3 million people died, and many observers consider it a genocide. The war's toll on women was also especially awful: Estimates say that at least 200,000 people were raped.

Recent investigations have also focused on the role the United States could have, and perhaps should have, played in ending the conflict. Pakistan was reliant on U.S. military hardware, journalist Gary J. Bass noted in his book "The Blood Telegram," but President Richard Nixon was fearful of using it, as Pakistan was a secret conduit for communications to communist China.

Ethiopia's Red Terror


Former Ethiopian president Mengistu Haile Marian in August 1990. (Aris Saris/AP)

Between 1976 and 1978, the Ethiopian government ran a brutal counter-insurgency campaign which they dubbed "Red Terror." Following the political vacuum created when Emperor Haile Selassie was deposed by a military junta in 1974, a new Marxist government, led by Mengistu Haile Mariam, sought to eradicate the Ethiopian People's Revolutionary Party and other opposition groups.

Estimates of those left dead vary greatly – Human Rights Watch says that the figure was "certainly well in excess of 10,000" and that the killings were "one of the most systematic uses of mass murder by a state ever witnessed in Africa." Other estimates say as many as 500,000 were killed.

Mengistu was deposed in 1991, and fled to exile in Zimbabwe. In 2006, an Ethiopian court found him guilty of genocide, though some doubt that the label is appropriate, as the killings did not target one particular group. Mengistu remains free in Zimbabwe.

See also

Why Israel does not recognize the Armenian genocide

Is this genocide? What four Americans saw happening to Armenians 100 years ago

Correction: This story originally stated that the number of deaths caused by the partition of India was in the hundreds of thousands. It has been updated to reflect a number of estimates that suggest the deaths were considerably higher than that.