It was the former Soviet Union that flooded ethnic Russians into Ukraine, as they did in all the other now-independent nations. As thou sowest also shalt thou reap.
Three scenarios:
Ukraine shot down the plane to blame the Separatists
The Separatists shot down the plane to blame Ukraine
Putin shot down the plane to gain a pretext to invade Ukraine.
If the third scenario is found to be accurate it will destroy any credibility that Putin still has around the world.
Nearly all the wars around the planet are the end-games in the unravelling of the old European empires. For example Iraq is the end game in the Middle East that was carved up the Treaty of Sevres when they dismantled the old Ottoman Empire, and the current borders of Iraq, Syria, Lebanon etc are totally fabricated. Similarly in the old Soviet Union, which was the second last Empire to fall... it was really still essentially an Empire until the 1990s.
It takes a couple of hundred years for these end games to play out. An interesting example is Central and South America (plus Mexico which is in North America) which was colonised mainly by Spain and Portugal. They were already old empires when Captain Cook went sailing. These empires have long gone, and it's noticeable that despite a couple of squabbles over the odd island or watershed in the Andes, all these countries rub along together ok in modern times.
Anyway it's bad news to wake up to.