In addition of Khmer, Inca declared war against me. Like that isn't pain enough, other civs demand tributes and cancellations of deals with their enemies. When I refused, they stopped trading with me. Frakkin' Hell! Never mind about that. Free religion improved relations all around and England even restored open borders. My riflemen have shot all invasive ground parties within 2 turns. As soon as I got military science researched, I started building ships of the line and those have steadily mopped off enemy frigates in my waters. I'm considering to invade Incas becouse they're closer and aren't as advanced as Khmer. I offered peace for both of them and Incas agreed to it, so never mind... I'm not the most advanced either, but I own military front with riflemen, ships of the line, and ironclads.
Trade with Ottomans got me scientific method which revealed oil in water tile at edge of my border. Gonna build some ironclads to guard my waters while I send ships of the line around to wreack havoc against my enemies (Khmer at the moment). Never mind, he's already got DESTROYERS!
It's all thanks to their land based oil supply while most others, including I, have it available only on water tiles! Frak! I have to give up on sea battles and focus on defending my main island. Workers are hard at work building railroads that will allow me to move footsloggers all across the island. When I upgrade my riflemen to infantry, even Khmer can't take my island. Damn stalemate... Still could restart war against Incas, capture their cities, and get more tax to fund research. But can perform effective war on two fronts? Likely not.
Then Sitting Bull demands tribute, and when I rejected it, he declared war. Guess what? His primitive army was no match for my ONE rifleman defending the city! But becouse America is on other side of the world, I'm not going to spend turns for counter invasion.
Greek declares war, Khmer brings tank and marines against my capital, and Russia has completed Apollo Program. If I had gone offensive against Khmer before they got destroyers, I might have stood a chance, but now it looks pretty much game over for me.