There is no definitive history of the post-Seattle anarchist movement. That's probably going to change in the next ten years and terms will be, for better or for worse, officially nailed down.
In a highly subjective nutshell: Contemporary anarchism comes out of 60's New Left Trotskyite and Maoist groupings so it has always had a tentative connection to Marxist or communist thought. It's beginnings are influenced by Murray Bookchin, Paul Goodman and others as well as a reintroduction of the anarchist thinkers and activists of the 19th and early 20th century. Roughly around 1975 there is a split in the "Fifth Estate" publication between anarchists influenced by Bookchin vs. groups like the "Love and Rage" collective who are influenced by the Situationists and others. But even here the split is an oversimplification as many of the positions overlap each other. By the 80's there is an eco-anarchist movement. By the 90's there is a merger of many eco-anarchists with the Zapatismo movement. All of this flows into the Seattle uprising. After Seattle there are explicitly anarcho-syndicalist or anarcho-communist organizations like NEFAC. 9/11 ends business as usual. The "Miami Model" in 2003 ends it even more especially in regards to Seattle and "Ya Basta" style confrontations with the police. The global uprisings of 2011 begins a revival of this trajectory.
This is not to say that there have not been major hostilities between anarchists and marxist/leninist/trotskyist/maoist groups. Some people on either side of the divide have defined themselves by that hostility. But I would say that that is more of an overall left predilection for vehement sectarianism than a particularly anarchist one.
This is also not to say that the revival of the post-Seattle anarchist trajectory sketched above is necessarily the most apt or authentic political response to the global uprisings of 2011. It's only the closest thing the US has had to an insurrectionary movement with a culture of direct confrontations with power.
The adoption or even the designation of any of this 2011 activity as anarchist could do with some scrutiny and critical thinking on the part of historians and commentators but I agree that in order to do that one needs to interview subjects that are a part of a mostly unwritten and undocumented social formation.
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