Although I had founded Confucianism and Christianity in my own territory, I decided to convert to Buddhism in 200 AD. The Celts, Germans and Chinese already had this religion by this point, and religion seemed like the best way to keep them all friendly while I fought the Spanish and Portuguese. Building the AP in 780 helped with that; although Brennus would be the first elected to lead it, I gathered more votes with missionaries and city conquests and would succeed him in 1220.
Brennus, Mao, and Bismarck joined me in the war against Isabella and Joao in 1130. (I didn't invite Catherine to join in, since I was already planning for her to be my next target and saw no reason for her to share in the "mutual struggle" bonuses.) In 1140, I completed the conquest of Spain. Portugal would hold out until 1440. By that time, Brennus had become my peace vassal.
I attacked Catherine in 1520, giving Bismarck some techs to join the fight. Mao joined in for free. Catherine capitulated to me in 1575. I then attacked Bismarck in 1590, captured three cities and vassalized him in 1610. With only Mao still independent, I achieved a Religious Victory in 1630, with 951 of 1139 votes in the AP.
Incidentally, both of my machine guns survived to the end of the game. Once the wars got under way in earnest, they became the defensive units for my attacking stacks. They weren't Humbaba, but they served their purpose!