Well, we've just seen Stephen Yaxley-Lennon (the guy who calls himself Tommy Robinson) formerly of the BNP and a founder of the English Defence League, try to make a march about antisemitism all about him.
Beware of situations that have been engineered to bring opponents together.
I think that's spot on. I think I've seen a lot of it in recent politics, but about groups rather than individuals. Group A realises it's never going to get groups X, Y, Z to like or support it; so instead tries to capitalise on moments when X, Y or Z are in conflict with some other group (for bonus points, in conflict with each other!), and attempt to claim common ground or to work together "for this issue only" – in the hope some of its material or networking will stick.
Obviously it didn't work for Yaxley-Lennon on this occasion, and he was unceremoniously seen off by the march organisers and police!
Some making of alliances happens naturally, of course. I've never been a fan of giving people a label and telling them they're on Team A and must believe all the Team A Manifesto and be eternal enemies of Team B.
But recently I've seen a lot of attempts at alliance-making which have marks of being engineered – including, where need be, engineering or at least fomenting the conflict in the first place. As someone said of the Orange Guy, he holds a puppy down in a bucket of water – then pulls it out and say, "Look, look, I rescued a puppy!" Similarly Russia attempts to recolonise Ukraine, burns and mines farmland, steals crops... and then turns up on the doorsteps of African countries which were formerly de facto under Soviet imperialism and says, "Look, look, we'll give you all this grain to rescue you from the famine caused by the West's war." See also propagators of male control and violence against women who are suddenly supporters of "women's rights" - courtesy of trans issues (though don't you be asking for any rights which might impinge on anyone important, little lady
).
So I think you're bang on about unholy alliances being key in our time. They just might not look exactly like Pompey & Crassus.
History doesn't repeat itself, but it does rhyme, etc.