Okay here's what happened to me. I was in a game with Egypt and I'm trying to take down England. At this point, I have Riflemen and Cannons. England is still using Musketmen and Longbowmen. But for some reason; I struggled to take the city. I did eventually take the city and England's capital once I got Artillery. I eventually ended up winning the game with a Science Victory. But why do I still struggle against Renaissance units when I'm using Industrial units? Did England have some sort of special promotion on their units or something?