Lyric discussion by ABookOnAShelf 

Cover art for Waco lyrics by Mountain Goats, The

Pretty clearly this is about the Branch Davidians. They were a group of Seventh-day Adventists who had broken away from the church and had a ranch/compound near Waco...they were led by David Koresh and were waiting for the second coming of Christ. Anyway, they were (legally) stockpiling weapons for the end of the world, and the ATF charged in there and both parties started shooting each other. Six of the Davidians and four agents died, and then after a two-month siege fires started that burned to compound and killed seventy six people.