Nowadays, Christian churches send missionaries off into the wilds to open schools and medical clinics and show the poor benighted savages the love of Christ via the miracles of modern medicine and suchlike.
Back in Medieval days, they used to saddle up in big posses like the Teutonic Knights or the Livonian Brothers of the Sword, and gallop at the heathen Slavs and pagan Balts yelling "Love Jesus or we'll cut your bleedin' heads off!" and then steal everything that wasn't bolted down and rape everything that was. (Apparently the Gospels had fallen out of their Bibles and thus the reversion to more Old Testament tactics.)
On this date in 1236, a bunch of Sword Brothers and their lightly-armed retainers and hangers-on were returning towards their home base from a few weeks of recreational looting, raping and proselytizing across Samogitia (modern Lithuania) when they were brought to bay at a river crossing by a large force of understandably pissed-off Samogitians, who proceeded to hand them a good old-fashioned pagan ass-stomping now known as the Battle of Saule.
Those knights that weren't killed on the spot were sent fleeing. Local tribes, already 'pacified' once, realized that the crusading knights weren't made of undefeatium and got uppity in a torches and pitchforks and hang-the-mayor sort of way. The Brothers of the Sword were finished, with the survivors being absorbed by the Teutonic Knights, and the bloody conquest of the Baltic states was set back by a good dozen years.