Russia’s army is among the biggest in the world and could overpower almost any other country on earth.
But the Ukrainian military is not tiny and has been bolstered recently by additional support from Nato allies.
Many inside Ukraine have also made it very clear that they are prepared to fight and have been seen training recently to prepare for combat.
Russia’s initial attacks have focused on destablising key military sites in Ukraine which has inflicted heavy damage.
It is clear however that the decision to invade will very likely result in a bloody conflict, with significant loss of life on both sides.
With the invasion under way, here we look at how the two countries’ armies compare.
Ukraine has around 125,000 troops in its army plus a further 35,000 in its airforce and 15,000 in the navy.
It also had 900,000 reservists at the last count, although it is not clear if this includes the many civilians who were being trained in combat in the weeks before the invasion.
In terms of firepower, the country’s military is thought to have more than 2,000 tanks and nearly 3,000 armoured vehicles.
It has around 200 attack aircraft including helicopters and just two warships.
Russia has around double the number of troops in its army, with 280,000, but has many more in its airforce and navy; 280,000 and 150,000 respectively.
Of these, it was thought there were around 190,000 troops massed on the border before the invasion began.
It also has significantly more firepower; nearly 30,000 tanks and armoured vehicles, 1,300 attack aircraft, 74 warships and 50 submarines.
As the country has had conscription since the end of the First World War – with all male citizens undergoing a year’s service – there are many hundreds of thousands reservists on hand if needed.
Russia is also the world’s biggest nuclear power, with 6,257 warheads according to the latest estimates.
MORE : Shocking photos show the aftermath of Russia’s overnight attack on Ukraine
MORE : Graphic reveals Russia’s nuclear arsenal compared to the rest of the world
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Russian forces have launched an attack on Ukraine, with swathes of the country – including capital city Kyiv, bring hit by rocket strikes.
Troops from Russia crossed the Crimea border into Ukraine in the early hours of February 24 after President Vladimir Putin gave the order for his invasion to begin.
Boris Johnson launched a scathing attack on the Russian leader as he unveiled a package of sanctions against the country, saying said Putin ‘will never be able to cleanse the blood of Ukraine from his hands’ and will be ‘condemned’ in the eyes of history.
He said President Vladimir Putin’s regime would be condemned to ‘pariah status’ after unleashing its ‘tidal wave of violence’ against its western neighbour.
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