1. Russian Troops Invaded Part of Ukraine This Weekend
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Over the weekend, Russian President Vladimir Putin ordered troops to go into a region of Ukraine known as Crimea. The military forces went in and surrounded Ukrainian military bases and, in some cases, took them over. There were no violent clashes.
Putin rationalized the invasion by explaining to Germany Chancellor Angela Merkel that he needed to protect ethnic Russians in Crimea from "ultranationalistic forces" in Ukraine. Crimea is made up of about 60 percent Russian people.
In plain language, Putin is arguing that a group of anti-Russian extremists now in power in Ukraine were a threat to Russian-speaking people who live in Crimea.
Putin's actions came after a change of power in Ukraine's national government last month when the country's Russian-friendly president, Viktor Yanukovich, left the country for Moscow and pro-European groups called for new elections.
2. The Struggle Over Crimea Is Partly About East-West Relationships
The political upheaval in Ukraine in recent weeks was partly about whether Ukraine would become more aligned with the European Union and the West or remain closely aligned with Russia.
The protesters in Ukraine's capital, along with about 12 percent of the population in Crimea that identify themselves as ethnic Tatars, wanted the government to become more pro-European. They succeeded in setting new national elections for May.
Yanukovich left the country for Moscow and sought Russian protection, which was quickly granted. Russia has said publicly it blames the West for trying to control Ukraine.
3. President Obama, European Leaders, and the United Nations Are Warning Russia to Back Off
President Obama has warned Russia "there will be costs" for any military intervention in Ukraine, and Secretary of State John Kerry has said "all options are on the table." Today a spokeswoman for the U.S. Department of State said economic sanctions are "likely" against Russia.
"So at this point we're not just considering sanctions, given the actions Russia is taking. It is likely that we will put those in place, and we are preparing that right now," Jen Psaki said.
European Union foreign ministers are meeting today to work on a response to Russia's military moves, one that could include economic sanctions. In addition, the United States is laying groundwork to kick Russia out of the G-8 due to the military action in Crimea.
The United Nations is sending a team to investigate the situation in Crimea this week, while NATO meeting Secretary General Anders Fogh Rasmussen called the situation a "breach of international law" and called on Russia to de-escalate the situation.
Countries including the U.S. have suspended their planning for the G-8 conference in response to Russia's behavior.
4. Russia Has Sent 6,000 Troops and Now Controls Many Bases, Buildings
Russia said it has sent about 6,000 troops into Crimea to protect Russian citizens, in addition to pro-Russian militias that were already in Crimea.
Together they have taken over parliament, the airports, and many government buildings. Troops have also surrounded or taken over many military bases, though not violently. A Ukrainian navy official tells ABC there are five Crimea bases plus naval headquarters in Sevastopol that have not surrendered, and they don't plan to surrender.
Today, Russian Prime Minister Dmitry Medvedev said he wanted to build a bridge connecting Russia to Crimea across a span of 12 miles.
At a Coast Guard base in Crimea, a soldier speaking to reporters said he was a contractor from Russia and that the surrender of the base had been emotional, not violent. Troops who supported Russia were seen hugging those who support Ukraine and were leaving. To add to the complex situation and emotions, one soldier standing out front, when asked whether he was Russian or Ukrainian, replied, "My grandfather used to say Ukraine is the best Russia has."
At the same base, Russia forced 15 Ukrainian naval ships to leave a Crimean port or surrender. They fled to Odessa.
5. The World is Waiting to See What Will Happen Next
Ukraine said today that it will not launch any military operations and pleaded with world powers to "give us time," but it has mobilized its troops to readiness levels.
Russia has not made any move to go beyond Crimea into the rest of Ukraine.
World leaders will decide on how to respond to Russia's military moves this week, which could include economic sanctions or more serious action.
The AP contributed to this report.