Once, I had established myself on my continent, with another, much larger one to be conquered. I had a beach head city and was in the process of shifting my large artillery/infantry army into position. A weak Inca was directly bordering the beachhead, while the French (weak) and Celts (less weak) were also sharing this continent, along with a Dutch civ that was stronger than mine. But, I was gonna need oil soon, my oil had just been exhaused and we were just starting to get the techs for tanks, planes, warships, etc. Inca had oil. Inca sucked. Easy pickings, right?
I had built a line of barricades along the border just in case, got my considerable forces to the continent, and was ready to go. I politely declared war with the Inca, and invaded their land directly after.
Unfortunately, theose 4 civs were rather close to each other. As in, "We all have MPPs and RoPs with each other" kinda close. So I didn't just invade the Inca. I began an enormous war with 4 of the 5 remaining computer players, one of which was significantly stronger than I. I still had no oil, meaning that I had just until the time someone else developed tanks to do anything before i was totally screwed. The Inca didn't even have to counter-attack; hordes of Dutch and Celtic and French infantry hopped on the train and went straight to the front lines, forcing my army to immediately retreat to the beach head city and pray that I could send reinforcements.
Oh, those barricades I mentioned? I forgot to actually put anyone in them. They really helped out the Dutch though.
Thankfully, I was able to inflict enough casualties to hold the line. The Celts and French ran out of units to send. I was able to steal a poorly defended oil reserve from the Dutch, and after they lost a large chunk of their army, they decided to offer peace, and then turned on the French to take their land before I could work my way over there. Once Papa William wasn't there to protect them anymore, the Inca fell rather quickly.