On Sunday, more than 100,000 Germans gathered in Berlin for a commemoration of the 25th anniversary of the fall of the Berlin Wall. Speaking at a memorial center, Chancellor Angela Merkel said: “We can change things for the better — that is the message of the fall of the Berlin Wall."

Merkel did not cite any examples, although she would have had plenty of choices. Today, dozens of walls and border fences continue to separate nations or territories across the world. Most of them were erected after the fall of the Berlin Wall, and there seems to have been a particular increase over the past decade.

According to data researched by Élisabeth Vallet, a scholar at the University of Quebec in Montreal, and visualized by The Washington Post, the number of walls worldwide remained stagnant after the fall of the Berlin Wall briefly. However, wall construction projects proliferated dramatically after the terrorist attacks on Sept. 11, 2001 -- reflecting instability in the Middle East and elsewhere. By 2011, more than 45 walls separated countries and territories.

Here is a selection of some of the walls and border fences worldwide.

India and Pakistan


An Indian Border Security Force soldier patrols near the fenced border with Pakistan in Suchetgarh on Jan. 14, 2013. (Mukesh Gupta/Reuters)

The rivalry between India and Pakistan —both nuclear-armed nations — dates to 1947, when British India was partitioned to create two states. Since then, they have waged three wars, including over the disputed territory of Kashmir. In 2003, partially as a response to the threat of militants infiltrating in from Pakistan, India started to build a fenced border with Pakistan after reaching a cease-fire agreement.

Georgia and South Ossetia


A barricade, part of a fence put up by Russian forces on the boundary between Georgia and South Ossetia, has been a source of dispute between Russia and Georgia. (David Mdzinarishvili/Reuters)

One year ago, Russian troops reportedly started to build a wire fence between Georgia and South Ossetia, the territory recognized by Russia as a sovereign state. In 2008, Georgia and Russia waged a war over the region that ended with the retreat of Georgian forces. The subsequent separation became particularly visible in 2013: A barbed-wire fence now effectively splits the village of Dvani, which is right along the demarcation line.

Gaza Strip and Israel


An Israeli police officer stands guard behind a barrier at the Kissufim checkpoint moments after Israeli troops sealed off the area. Signs in English and Hebrew hang on gates blocking the road into Gaza. (Getty Images/David Silverman)

The 40-mile-long border between the Gaza Strip and Israel is protected by Israeli guards and a barrier erected in 1994. There are only a few checkpoints where citizens can cross the border.

Egypt and Gaza Strip


A picture taken Oct. 26 from the Palestinian side of the Rafah border crossing in the southern Gaza Strip shows an Egyptian soldier (background) manning a watch tower on the Egyptian side. (Said Khatib/AFP via Getty Images)

Egypt agreed, based on a 1979 treaty with Israel, to set up a buffer zone between its territory and the Gaza Strip. Israel later built a barrier of metal, concrete as well as barbed wire. After Israel pulled out of the strip in 2005, an agreement was reached to deploy Egyptian guards to prevent militants or smugglers from crossing the border.

To stop smugglers from using tunnels, the Egyptian government started to build an underground metal wall in 2009 — a project condemned as a 'wall of shame' by many Arab commentators, who criticized the close cooperation between Egypt and Israel at that time.

Israel and West Bank


A molotov cocktail explodes next to the separation barrier as Israeli security forces take up positions during clashes with Palestinians stone throwers from West Bank on Oct. 13. (Atef Safadi/European Pressphoto Agency)

Twelve years ago, Israel started to build a 420-mile-long wall that separates the country from the West Bank. It is five to eight meters tall and varies in form: Some parts are built with concrete, others with wire. The Israelis argue that the wall has decreased the number of suicide attacks on their soil. Many Palestinians, however, view the barrier as an obstacle to their dream of establishing a viable state of their own.

U.S. and Mexico


A U.S. Customs and Border Protection agent patrols alongside members of the California National Guard at the U.S.-Mexico border fence. (Denis Poroy/Associated Press)

In 2006, construction started on a border fence separating the United States and Mexico after violence, drug-related crimes as well as illegal immigration surged. President Obama suspended parts of the project in 2010 to focus on technology upgrades.

North Korea and South Korea


A barbed-wire fence decorated with ribbons bearing messages wishing for the unification of the two Koreas is pictured Oct. 31  near the demilitarized zone separating North and South Korea in Paju. (Kim Hong-Ji/Reuters)

About 60 years ago, a demilitarized zone was established between South and North Korea. To protect the zones and to prevent citizens from crossing the border, a barbed-wire fence was set up. The demilitarized zone is 150 miles long and about 2.5 miles wide, and it has become a tourist attraction to some — but a sign of separation to many others. In the past few years, several people have been killed trying to cross the border illegally. It's considered one of the last frontiers of the Cold War.

India and Bangladesh


A villager sits with his grandson as Indian Border Security Force soldiers patrol in Lankamura, India. (Ramakanta Dey/Associated Press)

India and Bangladesh share about 2,500 miles of border. In 1986, the Indian Parliament approved the construction of a border fence to supposedly prevent illegal immigrants from entering — construction began in 1993. The confusing path of the boundary, which winds through rivers and marshy islands, leads to numerous incidents and border clashes every year. More than 700 Bangladeshis were killed along the eight-foot-high fence from 2000 to 2007, according to the Guardian newspaper.

European Union


A fence runs along the Bulgarian border with Turkey near the village of Slivarovo. (www.politicalbeauty.com via AFP)

The European Union has erected several fences that are supposed to prevent Middle Eastern and North African refugees from reaching a member state of the union. Last week, German political activists belonging to a group called "Center for Political Beauty" claimed they had stolen Berlin Wall memorial crosses and relocated them to several E.U. border fences to draw attention to the fate of those dying while trying to flee to Europe. Tens of thousands of people have died trying to cross the Mediterranean Sea in the past few years.

Spain and Morocco


A Spanish Civil Guard officer pulls an African migrant from a border fence as he tries to cross into Spain's North African enclave of Melilla from Morocco on Oct. 15. (Jesus Blasco de Avellaneda/Reuters)

One fence that separates E.U. land from other countries is in North Africa. There, the Spanish enclave of Melilla borders Morocco, where refugees continue to try to breach the modern rampart.

Cyprus


A wall marking the boundary of the U.N. buffer zone is seen from the Greek Cypriot-controlled area of central Nicosia on March 10. (Neil Hall/Reuters)

Cyprus, located south of Turkey, is separated by a U.N. buffer zone established in 1974 and a wall. It divides the Greek Cypriot-controlled south of the island from the north of the island, which is recognized as an independent territory by Turkey.

Ireland


A section of the wall that divides Catholic and Protestant communities cuts its way through West Belfast on Oct. 3. (Cathal McNaughton/Reuters)

In Northern Ireland's Belfast, "peace walls" still separate Catholic and Protestant communities. Currently, there are 99 barriers in Belfast alone, as well as similar walls in the city of Derry.

Morocco and Western Sahara


Moroccan soldiers stand behind a fortified "sand wall" that seals Moroccan-controlled areas of Western Sahara near the Algerian border on Nov. 6, 2006. (Francois Mori/Associated Press)

Western Sahara — a disputed territory in North Africa — is sealed from Morocco by a sand wall . It was built in 1987 to stop attacks from separatist troops in Western Sahara. Trenches, barbed wire, land mines as well as a substantial number of soldiers still guard the decades-old border area.

Baghdad


A painter decorates a security wall sealing off the southern section of the Shiite enclave of Sadr City in Baghdad. (Karim Kadim/Associated Press)

In 2007, the U.S. government pursued the idea of building a wall within Baghdad to separate neighborhoods that are predominantly Sunni or Shiite. Back then, the three-mile-long wall was supposed to be temporary, but it remains in place even today.

There are even more walls and barriers

These are just a selection of the world's walls. The border between Botswana and Zimbabwe is separated by an electrified fence. Malaysia and Thailand are separated by a wall, as are Saudi Arabia and Iraq, Iran and Iraq, and Kuwait and Iraq.