More than getting off their bongs, Bro, it was the fall of communism that has neutralized the matrix of extreme left terrorism in the West.
The victorious neoliberal regime and a not fortuitous multiculturalism (I say not fortuitous, because of the way globalization under the sway of economic liberalism has fashioned it), has led to mass exclusion and hardship among the established citizenry, such that a militia - which is what the Tea Party and NRA (sic!) more properly speaking are (you used the appropriate term "war like") - menatality has set in to defend the homestead from the federal government ("socialist boogeyman") and those f-ing immigrants (the impure) who are stealing our jobs, who are thus the scapegoats of their (often perceived more than real) misery.
If the 60's and 70's were the hey-day of a social revolutionary cause that had led some, in their psychosis, to believe that only through violence would that utopic, better world under disingenuous epithets like "peace and love" they longed for be realized; today you have rage fueled folk propelled by purifictory, eschatological and messianic (often influenced by evangelism and para-religious banter) toward a different kind of revolution: namely the reestablishment and purification of the "true America" to give the white man (the pure) back his lost dignity.
That this is an extreme right phenomenon, one which has thus been radicalizing the conflict, and completely estranged from the left there can be no doubt. While it’s the biggest internal problem the US faces and is completely home bread.
PS: The reports I've been reading say that the official investigation believes this wasn't Al Qaeda, but a home spun attack. The first, unfortunately, of many to come no doubt in this climate. Of course a corolary to the phenomenon are the instances of mass murder with private arsenals in the name of a "right to bear arms." These too are destined to continue.