I thought they'd just announced a cease-fire. 
I think that has been done with a metaphorical gun held to the Ukrainian president's head, where the Ukrainian army has been winning in East Ukraine, but they are no match for a full Russian onslaught. Russia will probably say, they have invaded on humanitarian grounds (they haven't, this is a land grab) to try to minimise the protests and sanctions from the West.
The Ukrainian president had a phone call with Putin, just before the ceasefire was announced. So there was probably something along the lines: You cause Russian casualties by resisting we will take over all of Ukraine, no resistance and we will just annex the East (and probably South-East), and we will leave you (probably for now) West Ukraine.

Russia is looking for a corridor to Transnistria to bring Moldova (by invading if necessary) back under their full sphere of influence, where Moldova are looking to join the EU and Nato.
The West is going to have to get very tough with Putin, where his next target is annexing the Baltic states. Again this will be, like in Ukraine, by using a 5th column, useful fools and unidentified, plausibly denied, green men etc. He is already trying to create unrest amongst ethnic Russians in these countries and squeezing them wherever possible economically. To stay in power where the economy and living standards have not been growing at a pace to keep Putin's key Russian officials happy with ever increasing living standards, he is going the alternative empire building route, to court popularity and to stay in power. With Crimea this worked with the highest ever approval rating of 80% by the Russian population.
The problems with this is that it is very easy to overstep the mark as you get over confident, like Hitler did with Poland and start a major European war and also the resistance trying to get back their country. Ethnic Russians are 17.3% of the population of Ukraine. Polls have shown the for the vast majority of Ukrainians (and many Ukrainian Russians) freedom and their right to self-determination is much more important than wealth. In Russia it is the reverse.
