The Christian church was born into the world at just the right time. One would almost think a sovereign God orchestrated history so that these secondary causes would be present for the spread of Christianity. As Christians, we can not only think such, we can confess such. Emphasizing secondary causes in God's role of spreading Christianity (or any other action) does not take glory away from God, rather it reinforces that He does receive His due glory.
Christians believe in a sovereign God who has all power, all authority, and who governs all. He is active. He does not sit idly in heaven and allow His creation to slip into chaos. He directs all things, governs all things, and sustains all things. This world and everything in it moves at His command. The church began with a few dozen or so individuals whose leader was crucified as a criminal. The disciples enjoyed no position or prestige.