I didn't read (or skim) the article, but there are recent examples. Chechen vets coming back to Russia and forming into what Russia calls "OPGs" Organized Criminal Groups. Now that I think about it, Mexico has this without the colonial wars in the form of cartel enforcers.

Then we had the US vet running around South America this year and embarrassing the US.

There are several examples of ex-troops assassinating presidents.

The French Foreign Legion started trouble in France when bored after multiple deployments.

I can think of probably a 100 examples.