...and US-led sanctions, as well.
My conspiracy theory is that the US called in a favor, decades in the making, from the Saudis, to flood the oil market and crush the Russian economy in response to their involvement in Ukraine. Russian troops had "complete control" of Crimea by March 2 2014, crude prices began to drop in June 2014, dropping from $107/barrel to $32/barrel over the next 1.5 years. The drop in oil prices hit Russia hard: