Midgame warmongering tips (Immortal)

I can capture an early citty or two with composites. I can use battleships and rocket artillery later in game if I am one of the tech leaders.

Anything inbetween I am lousy at. never know when to sacrifice science and infrastructure to push down the melee unit paths.

Doesnt help that I suck at playing wide too. 3-4 tall cities is my norm.

Any advice?

I've started playing a lot of multiplayer with me and my brother and 5 AIs that we gang up on. He always goes wide and I go tall , and he wrecks me points wise every time. Liberty tree is soo much better than tradition or honor could ever hope to be.

If you can take a few puppets early then this should set you up fairly well for mid-game. Basically you have 2 good options at this point - start developing your cities and push science hard (beeline Education, etc.) or continue on with warmongering using your now well-promoted army and upgrade when possible (e.g., spears to pikes, comp bows to crossbows, swords to LS/muskets). Either way should work depending on the map and your general strategy. But even with option 2 you don't want to completely neglect science or you will fall behind.

after composites/warriors/spears lose their punch your next wave is Crossbows/swords/pikes

If you grab enough solid targets with CB's, you should be able to hold off on science/infrastructure. Just push straight into longswords. I find domination games to be less about keeping up with the AI and more about tearing them down.

Going wide can help keep up science with less focus on the top half of the tech tree. Science is largely tied to population, and you can get more raw pop. from going wide as long as you can cover the base cost of settling a city.

Beeline for Crossbowmen after Education - in most cases you will beat your nearest neighbour unless they also have Machinery - which is unlikely unless it's China/England. Any city without a Castle is pretty much gone with the CBs you've upgraded into Crossbowmen. Pikes are decent enough to survive 1-2 turns to take the city.

Gatling Guns is the next stage, they come at a good time when you usually unlock Communism for a boost of happiness to continue warring. Or Cannons, but I find Crossbowmen are good enough to last through until you get Gatling Guns.

Unless those CB's are covered in promotions, I find it better to transition into cannons. Gatling/Machine are great for breaking up infantry live vs. infantry line, but when it comes to actually taking cities, the cannon~>artillery line is vastly superior. The game at this point tends to break down into attrition, and the ability to drop cities quickly and efficiently once they are in range is huge.

Hang in there, produce a lot of military, keep your best safe, rotate in and out of the war zone to healers.

start early defensive war by fast settling near neighbours with 3-4 archer till get range or logistics. next upgrade them to CB/XB you'll be fine onwards.