[throehtjr]

Read about Avar, Mongol, Tatar, Turkish... invasions. This is very common tactic, going all the way back to Alexander the Great.

They were not burning capital "out of spite". Not everyone is like French who surrender Paris to protect art.

[hef19898]

Nothing about your last your last sentence is corewct, actually. And partially about ypur first one as well.