The battle for Donbas: What's behind Russia's new Ukraine offensive

ON THE ROAD TO KYIV, Ukraine — For weeks, Ukraine and its Western allies have been waiting for Russia’s promised offensive in the Donbas — an eastern region of the country that borders Russia — in the wake of Moscow’s hasty retreat from around the capital, Kyiv.

Now, that offensive has begun.

With troops concentrated for a major ground assault, airstrikes bombarding cities and Ukraine’s forces steeling for what could be a series of decisive battles, many expect the Russian offensive to be better equipped and organized than the failed first phase of the war.

So why has Russian President Vladimir Putin refocused his military's efforts on this region of eastern Ukraine, and what should we expect in the days and weeks to come? NBC News takes a look.