More precisely, he will attempt to get Greece into bankruptcy - the situation before the elections was relatively sustainable (AFAIK), as far as the debtors are concerned, but the problem was that Greece and its people were being sucked dry - taxes increased, spending cut, public companies firesold, widespread unemployment (25%, youth 50%), GDP collapse (20%). Greeks didn't want to live like this (would you), especially since only they were suffering, not the institutions that were lending them the money in the first place ("every addict has a drug dealer").
The new party, Syriza, which Yanis is a part of, is trying to reduce the debt burden in a way that would be acceptable to the rest of EU, e.g. by shaving off part of the debt / delaying the repayment / restructuring it so that it's only paid when the economy grows (as German debt after WWII) - which technically is a bankruptcy.
