Obama Ukraine/Russia 2014
President Obama's speech on Wednesday in Estonia, a small eastern European country that reasonably fears it could be next on Russia's invasion list, was a huge step against Russian aggression. Obama promised that the US and the other members of NATO (a military alliance that includes most of Europe) would fight to defend any invaded member state, including Estonia, as if it were "Berlin [or] Paris [or] London." That is a big deal, meant to deter Russian aggression with the ultimate threat: war against the United States military.
But there was another message in Obama's speech, one that was in the subtext but came through loud and clear, especially to Ukrainians: the United States and NATO will not defend Ukraine from the ongoing Russian invasion pushing across its border. The US is not exactly abandoning Ukraine — it still wants to help — but it is not going to do anything that would force the Russian invasion to stop.
https://www.vox.com/2014/9/3/6102001/obama-abandons-ukraine