On February 24, Russia invaded Ukraine. It is the biggest attack on a European country in 80 years.
Ukraine was once part of the Soviet Union, a group of countries controlled by Russia. When the Soviet Union broke up in 1991, Ukraine declared its independence.
Russian president Vladimir Putin wants Ukraine back. In 2014, his troops took over Crimea, a southern province of Ukraine. Russia also backed a conflict in southeast Ukraine that has killed 14,000 people.