War with Russia has loomed over Ukraine for more than eight years – from crippling cyber attacks to the seizure of the Crimean Peninsula in 2014 and the long-running conflict in the east that has claimed more than 14,000 lives.

On Tuesday, Russian President Vladimir Putin officially recognised breakaway rebel provinces in the east as independent and rolled in his own troops. The West warned this was the start of a full-scale invasion of Ukraine, and a rain of tougher sanctions on Russia has begun to fall. NATO is also bolstering its troops in neighbouring allied countries.

Here are three maps that explain why Ukraine is so important to Putin, why he’s accusing NATO of “encircling” Russia and how a war might play out.

Why does Putin claim Ukraine is Russian?

This pink sprawl is the former Soviet Union. It took in Ukraine but as it broke apart in 1991, Ukraine and other republics in the union became independent, rewriting Russia’s boundary to the red line of today. (Wedged between Lithuania and Poland is the Russian exclave of Kaliningrad.)

With the Black Sea on its doorstep and a host of NATO countries to the west, Ukraine lies on an important crossroads in Eastern Europe. It’s one of the largest countries in the region, with a population of 44 million and one of the largest militaries. The capital, Kyiv, is considered the birthplace of the Rus empire that became modern Russia, although the territory has been ruled by many powers, including the Mongols and Ottomans. There are still deep ties to neighbouring Belarus as well as Russia, but most Ukrainians consider themselves a separate people.

To Putin, Ukraine is still part of Russia and cannot fall to the West. For much of Eastern Europe, it’s also a red line. If Russia reclaims one ex-Soviet state, will it come for them next?

Why is this also a showdown with NATO?

Putin calls the collapse of the Soviet Union in 1991 “a major geopolitical disaster”, which saw Russia lose “40 per cent of our territory”. He questions why NATO, the North Atlantic Treaty Organisation formed after World War II to contain the Soviet Union, has continued to expand since the USSR broke apart.

Putin wants NATO to disavow talk of Ukraine ever joining the alliance, and pull back military forces in Eastern Europe, effectively rewriting boundaries agreed between NATO and Russia in 1997. Since then, more than a dozen countries in the region have joined NATO, including the former Soviet Baltic republics Estonia, Latvia and Lithuania. In 2008, when NATO declared its intent to bring Ukraine, Georgia and Moldova into the fold, Moscow said a red line had been crossed and Russia had “nowhere further to retreat to”. In 2008, the US lobbied to let Ukraine and Georgia into the alliance but was blocked by Germany. In the years after, both Georgia and Ukraine were invaded by Russian forces.

While Ukraine is unlikely to join NATO soon, experts say Putin is determined to bring it back into Russia as he looks to reclaim some former Soviet glory and expand his “sphere of influence” in Eastern Europe. He’s even set up a loose military alliance of his own with Belarus, Armenia, Kazakhstan and Tajikistan, and has positioned troops in Belarus, a three-hour drive from Kyiv.

What are the Ukrainian territories Russia has invaded?

When revolution in Ukraine toppled its pro-Kremlin president in 2014, Putin sent in his “little green men” – soldiers without insignia – to seize the Crimean Peninsula. Shortly after, Russian-backed separatists in Ukraine’s eastern industrial heartland of Donbas took over government buildings in the cities of Donetsk and Luhansk and parts of the surrounding regions of the same name, igniting an eight-year war.

Both Crimea and Donbas are home to a large number of Ukraine’s ethnic Russians and Russian-speakers. Public sentiment about the Kremlin there is mixed, even as people in the country’s west and Kyiv denounce the territory grab. Putin claims he is defending Russian-speakers, many of whom have been issued with Russian passports in recent months, but the West warns Russian reports of Ukrainian attacks in the east are part of “false flag” sabotage plots by the Kremlin designed to sow violence and offer a manufactured pretext for war.

Russian troops inside these eastern territories are a violation of international law, world leaders say, and the start of a further invasion of Ukraine that began with Crimea in 2014. Putin has said that the separatist territories extend throughout the wider regions of Donetsk and Luhansk that the rebels have laid claim to – including land held by Ukrainian forces – raising fears of an invasion beyond the “line of contact”, a 500-kilometre frontline simmering with sniper fire and rocket shells.

Meanwhile, additional Russian warships are moving in the Black Sea near Crimea and some experts warn Russia may be planning a pincer movement, attacking Ukraine with forces from Belarus in the north, from the east in Donbas, and from the southern peninsula.

But they face a Ukrainian army that has grown since the undeclared war in the east broke out, and civilian militias that have swelled as weapons flood in from the West.