What kicked it off? Putin's invasion of Crimea?

That seems like a pretty good point of reference, yeah, but a lot of things had been going on, and things continued to heat up after that. Shrub's unprovoked invasion of Iraq without UN authorization, Euromaidan, the Arab Spring, Daesh, the invasion of Libya, the civil wars in Sudan and Congo, Cablegate, the Snowden revelations, and of course the ongoing tension with Iran. The next year the US began open hostilities with the PRC over supercomputing, stopping the expansion of Tianhe-2, though infosec warfare had been ongoing for years.