Eastern Ukraine was added to Russian Empire in 1654-1667 with western border defined by River Dniper. These parts were first incorporated into the Ukrainian territories in 1919-1920 and then in 1922 Treaty that created the USSR. Here are the lands lost in the Polish War by Polish-Lithuanian Commonwealth and gained by Ukraine via Russia: http://en.wikipedia.org/wiki/File:Polish-Lithuanian_Commonwealth_1635.s…
Today's Western Ukraine was formed during one of the subsequent three partitions of Poland: http://en.wikipedia.org/wiki/File:Rzeczpospolita_Rozbi which also added significantly to the Ukrainian territories claimed today.
In 1783 Russia added Crimea and other parts of Tatar Crimean khanite, including Odessa.
Irony has it, as http://www.britannica.com/EBchecked/topic/612921/Ukraine/30071/Ukraine-… points, it was Russian imperial control that allowed Ukrainians to settle into Crimea and Southern Ukrainian territories.
After WW2, Soviet Union largely expanded Ukrainian territory adding over 65,000 square miles and 11 million population (an increase of over 1/3 on pre-war period. The main expansion took place along the Curzon Line at the expense of Poland, Romania, Czechoslovakia.
Lastly, in February 1954, Russian Republic (RSFSR) 'gifted' Crimea to the Ukraine - from legally Russian territory (sub-part of the USSR). Only 22% of Crimean population at the time was Ukrainian (the rest were Tatars, other ethnic minorities and those, who Kiev supporters today frequently call post-genocide occupants of Ukraine coming from Russia, but in reality are Russian ethnicity residents of Crimea and Eastern Ukraine since 17th century).
Here is a summary map of what shaped the territory of the Ukraine prior to 2014:
These changes in the territories clearly indicate that ethnically Russian population is not a phenomena of colonisation post 1922 famine, but an outcome of centuries old movements of people with changes and reshaping of national, political, economic and cultural boundaries.
Alas, with every day passing, this hope of a unified Ukraine is becoming less and less feasible in the longer run and Kiev's insistence on avoiding orderly, democratic federalisation now threatens to lead to a civil war in the short run.