Any tips for stopping the green tide? I'm playing as lizardmen and north of me the greenskins expanded unchecked for a good 100 turns. I thought I had better intervene before they got too out of control but I fear I might have been too late. For every stack I kill three more march down from the mountains. They've broken through my front line and there are armies roaming around my territory sacking and razing everything. I have no problem fighting them, one of my stacks can wipe 2+ of theirs, but they seem to build them up faster than I can knock them down.
Just kill their stacks. Greenskins have a snowball mechanic, which is fightiness. If their armies start to win victories they'll get leadership bonuses and also spawn large waaagh stacks which will reek even more havoc. On the other hand if you defeat them and force a retreat they'll end up at low fightiness, suffering attrition. Also unlike lizardmen (who can dump near-infinite amounts of money into making their buildings better) Greenskin buildings kinda suck and their passive income isn't going to be amazing. They're a hybrid of a horde and a normal faction, and need to keep conquering things to sustain their armies. If you push them back eventually they'll run out of steam. Also on the topic of them being a horde, as lizards you'll want to defend river crossings and mountain passes. The Greenskin AI is absolutely confident and aggressive enough to attack you on those and you'll get the maps with two little bridges, allowing you to use sauruses/dinos to take out their calvalry, negating their best advantage.
My rule of thumb for fighting Greenskins is as long as I'm taking territory *somewhere*, that's a win. Even if its one army taking one settlement every 10 turns. As long as you're making some kind of progress and they aren't, at some point things will snap into place and you'll start annihilating them.
For what its worth, fighting Greenskins is the #1 form of diplomacy in the game. Everyone in the area will love you, like expect to meet Skaven and Undead with happy little green faces and "+200: military actions against Greenskins". Try to leverage that by getting allies, which will give you vision. Keep track of who looks like they're in danger and who isn't fighting the green tide, give the latter military coordination goals on a settlement and eventually they'll send a stack over to say hi. It'll keep the heat off of you. Also if you haven't already, get a port on the west side of the continent (you're Last Defenders, right?) and make trade deals with everyone. There's a lot of money to be made there, especially for lizardmen who get a trade good off of gold in addition to the gold itself. Which BTW scout around a bit and find settlements that have gold, since Greenskins don't trade and their eco buildings aren't good, stealing (or razing) their gold mines will create a huge income swing in your favor.