Russia's Plan A in Ukraine failed. Here's what Plan B could look like

Ukraine's military has fought so effectively that Russia has abandoned its Plan A, which envisioned a quick takeover of the capital Kyiv. Russia has now turned to Plan B, with troops focused on the eastern part of Ukraine.

So as the war enters a new phase, what does this mean for both sides?

The advantage of fighting at home

Ukraine has so far made the most of one key asset during times of war — the home-field advantage. "People are motivated to defend their territory when it's their home turf, more than people are motivated to attack it," said is with the Council on Foreign Relations and the author of "You can see that the soldiers and the mercenaries on the Russian side are not particularly motivated, whereas the Ukrainians defending their homes are." An invading army like Russia has to pack everything it needs — weapons, fuel, food, medical supplies. And Russian troops have been sleeping outside for weeks during the rough Ukrainian winter. As Russia regroups, it's concentrating forces in eastern Ukraine, just across the border from Russia. That could improve its troubled supply lines. But at the American Enterprise Institute believes "the Ukrainians will still have big advantages."