I'll tell you a story.
In the year 1099, a bunch of French, German, Norman, and Italian folks, at the request of Pope Urban II, marched from Europe to Jerusalem. Their mission, to rid the 'Holy Land' of unbelievers in the name of the Lord and justice. The Pope financed their mission and sent them walking east to Constantinople.
The reason they went to Constantinople was that when Rome Empire divided itself in to two kingdoms, Rome in the West and Constantinople in the East, called the Byzantine Empire, the part of the Roman Empire that stayed intact was Byzantines. While Rome and the rest of Europe suffered through the Dark Ages, the empire in the East prospered from trade with Muslim and other Eastern kingdoms. They were rich, sophisticated, had advanced technology, and had culture coming out of their ears. The European crusaders on the other hand, were poor, dirty, hairy, illiterate and lacked manners.
So, when those poor crusaders marched up to the gated of Constantinople demanding they help them in their mission to rid the Holy Land of infidels, the Byzantine's freaked. The smelly rubes didn't even wear perfume and jewelry as the Byzantines men did and they stole everything that wasn't nailed down (and some stuff that was). It was like having a mob from say ... Honduras, march up to your front gate and demand food, housing, weapons, and soldiers to go off and help them fight their war.
So, the Byzantines said, 'Yeah, sure ... we'll help you slaughter the infidels. We will transport you across the Bosphrous River and point you at the infidels. Go get 'em boys'. The crusaders took them up on it, and gleefully went into what is now Turkey to do the work of the Lord. The thing is, the infidels they slaughtered were Coptic xtians who the Byzantines considered to be heretics.
That was the beginning of the Crusades, a series of wars lasting from 1099 to 1453 when Constantinople fell to the Turks and the Ottoman Empire began (lasting until 1918).