Ukrainian forces launched a surprise attack into Russia’s Kursk oblast on Wednesday. The incursion occurred from near to the Ukrainian city of Sumy in the country’s northeast. Ukrainian forces have pushed between 5 and 15 miles into Russia in some areas. The local governor decried a “difficult operational situation” on Wednesday evening.

The question is, why? Why did Ukraine do this? Beyond aggravating Russian President Vladimir Putin, what purpose does this action serve?