I have to wonder what the historical practice has been regarding evangelizing a new land.
I don't want to sound like TomS here (
), but usually missionary activity was linked with worldly circumstances. We consider Sts. Cyril and Methodius Orthodox saints, for instance, but they actually sought help from that dreaded Roman Church at a time when it was technically in schism, and had broken communion with the Local Church of Constantinople, who had sent these saints to missionize the Moravians in the first place. St. John Chrysostom missionized many in Turkey, and I believe Georgia and Armenia, ordaining clergy for them and having texts translated into their tongue... but this happened because he was being sent into exile (though St. John had, admittedly, sent missionaries to various regions while he was Patriarch).
Bulgarian Prince Boris, when deciding who to allow into Bulgaria as missionaries and clerics (Constantinople or Rome), based his decision on things like which group would give Bulgaria an autonomous Patriarch the quickest. Prince Boris went back and forth a few times, before he finally made up his mind. The fact that Constantinople and the Byzantine army were right next door--and that the Emperor had threatened Bulgaria should they make the wrong choice--probably played some small part in who Bulgaria eventually chose.
Even if we consider the Scripture, when was it that the Jewish Christians started missionizing outside of Jerusalem? "And at that time there was a great persecution against the Church which was at Jerusalem; and they were all scattered abroad throughout the regions of Judaea and Samaria, except the apostles... Therefore they that were scattered abroad went everywhere preaching the word." (Acts 8:1, 4)
So I guess the answer, from what I understand, is that whoever gets there and is strong enough (either politically, militarily, or religiously) to keep their claim strong, gets to claim the fruits of God's work as their own (ie. they get to claim that they--and not those other people--were the instruments of God). Man, I sound cynical tonight!