Russia’s attempt to stop Ukraine leaving its sphere of influence goes back years, and its initial invasion began in 2014 when pro-Russian president Viktor Yanukovych was ousted after months of mass demonstrations.
Yanukovych had abandoned an EU deal under Putin’s pressure, prompting protests that ended when snipers shot dead dozens of demonstrators. Yanukovych soon fled to Russia.
Putin quickly seized Ukraine’s Crimean peninsula and Russian proxies took up arms against the government, occupying parts of the eastern Luhansk and Donetsk regions.
Two attempts to stop the war came to nothing.
They were known as the Minsk agreements and were brokered by France, Germany and Russia itself. They reduced the scale of violence, but Zelensky has called them a trap that created a frozen conflict on Russia’s terms.
Both sides accused each other of violations, and the Kremlin said ultimately the failed accords were a precursor to Moscow’s full-scale invasion.
The Ukrainian leader has warned the Trump administration not to trust Putin: “He broke the ceasefire, he killed our people.”
Who is winning the war?
After more than three years of offensives and counter-offensives, Russian and Ukrainian forces are in a war of attrition on an active front line of more than 1,000km (629 miles).
Neither side has any realistic prospect of winning this war, although Zelensky has warned that Russia is preparing a fresh offensive in the north-east.
Russia annexed four regions in eastern and southern Ukraine after sham referendums in 2022, and yet it can really only claim to have full control of one of them, Luhansk.
Ukrainian forces were able to liberate large areas of the north and parts of the south in 2022, but more recent counter-offensives have not had the same success.
They remain active in a very small part of Russia’s Kursk region after launching an offensive in August 2024, but have lost control of all major settlements there. Ukrainian troops have also lost ground in the east.
Much of Russia’s firepower has been turned towards the Donetsk region, as towns and villages are destroyed in a slow and grinding advance.
The war is taking its toll on Russia’s economy, with high interest rates and inflation and defence spending this year of at least 33% of the federal budget.
Ukraine has lost a big part of its economic wealth to Russian occupation and destruction in its industrial east. Growth has been hit by attacks on its energy infrastructure.
Although inflation and interest rates are high, Ukraine has secured Western aid to cover its budget deficit.