Ultimately, it's about power.
When Ukrainian President Viktor Yanukovich suspended an agreement with the European Union (EU) on November 21, his personal considerations would certainly have been a driving factor.
Signing the agreement would not only have brought Ukraine much closer to its Western neighbors. It would also have made its political sphere more democratic and competitive and its economy more transparent -- outcomes that would have been unlikely to fit with Yanukovich's personal interests.
What the EU did in the past with its enlargement policy, and what it is trying now to replicate with its "Eastern Partnership", is to use its economic power as a tool to push neighboring countries towards liberal democracy.