This is probably as old as the notion of diplomacy between political entities. The Assyrians frequently claimed to have gone on a military expedition because someone had attacked their allies, and they were just stepping in to protect them. The claim was probably self-serving propaganda in most cases, but it shows the existence of the concept.

Among the Classical Greeks, this was pretty much the only way wars broke out. Major states rarely simply attacked each other, even if they'd been sitting on a host of slights and growing resentment for decades. Outright war only came about as an escalation of a conflict between smaller states that happened to be part of the alliance networks of the opposing sides.

At least as early as the 4th century BC (and probably a lot earlier), it was established practice to provoke war by forcing your opponent's proxy to attack your own proxy, so that you could claim to be marching to war in the righteous defence of an ally. Wars of "intervention" were a great way to make the enemy look like the agressor.

Example: the Thebans triggered the Corinthian War (395-386 BC) by persuading their allies in Locris to levy a tax on a piece of land that was claimed by the Phocians, who were allied to the Spartans. The Phocians predictably retaliated with a raid on Locrian territory. The Thebans declared that the Phocians were out of line and counterattacked, at which point the Phocians appealed for Spartan aid. This was how Thebes managed to achieve its goal - war with Sparta - without ever looking like it had simply attacked Sparta without provocation.