The roots of the current standoff in Crimea go back a few days, and weeks, and years, and centuries. Here's a look at how the situation evolved; my 486 words, not counting captions, start now:

A Russian service member guards the Belbek airport Tuesday. (Vasily Fedosenko/Reuters)

What has happened in the past few days
Thousands of Russian troops have entered Crimea, a peninsular portion of Ukraine with strong ties to Russia and which is home to Russia’s Black Sea fleet. Ukraine’s interim government has called this an invasion, and U.S. and European officials have warned Russia that it will face consequences if it doesn’t withdraw. Russian President Vladimir Putin said that the troops aren’t Russian but that he has the right to send in troops.

Protests in Kiev on Feb. 20. (Volodymyr Shuvayev/AFP/Getty Images)

What happened in the previous two weeks
Protests (explained below) in the capital of Kiev had looked like they were dying down, but then a measure in parliament to limit the president’s powers stalled. Protesters were angered, and police responded; scores were killed over the next few days.
Protest leaders and then-President Viktor Yanukovych came up with a deal to hold elections in December. Parliament also took action, slashing a lot of the powers the president had.
As the opposition gained power, Yanukovych fled Kiev for Russia. Photos of his mansion and fabulous car collection went viral. Yanukovych insists that he’s still president, but the opposition has set up an interim government and set elections for May 25.

Ukrainians wave an E.U. flag on Nov. 22. (Sergey Dolzhenko/EPA)

What happened three months before that 
Yanukovych announced that Ukraine would seek increased cooperation with Russia, a sign he was moving away from Europe. This angered some Ukrainians, and they took to the streets in Kiev’s Independence Square, also called the Maidan. Protests largely took place in Kiev and in other cities in the Europe-leaning western part of Ukraine.

Ukrainians protest election fraud on Nov. 2, 2004.

What happened nine years before that
In 2004, Yanukovych won a flawed presidential election, and Ukrainians filled the streets to protest. Thousands demonstrated in what was known as the Orange Revolution. A new vote was ordered, and Yanukovych lost. (He won the presidency in 2010, however.)

Soviet army cadets register to vote in 1991. (AP)

What happened 22 years before that 
Ukraine got its independence when the Soviet Union collapsed through a 1991 referendum. The country is about as big as Texas with about twice half as many people. (Corrected March 5, 7:20 a.m.) At that point, 54 percent of voters in Crimea favored independence from Russia. The peninsula created its own constitution and legislature and has a significant amount of autonomy.

Kiev in 1962.

What happened about four decades before that
In what was considered a gesture of goodwill, in 1954, the Soviet Union transferred ownership of Crimea to the Ukrainian Soviet Socialist Republic, which was formed in 1922.

What happened two centuries before that
Catherine the Great, in the late 1700s, developed coal and iron industries in what is now the eastern part of Ukraine. She later took the west on as well, but she and other Russian rulers were mostly focused on the fertile land of the east, compared with the forests of the west. Russians moved into southeastern Ukraine to battle the Ottoman Empire and banned the Ukrainian language. Russia managed to keep the peninsula as part of its territory even after losing the Crimean War.

Some more helpful files on Ukraine:

What Russia's Black Sea Fleet in Crimea looks like

Why Ukraine's military might not be so easy to crush

Why this isn't like the Georgia-Russia situation of 2008

Why protesters have been called fascists

The complicated history of Crimea