Complex sentence: Meanwhile, Americans tried diplomatic channels to legalize Christian missionary work, and in 1869 two outposts had been established: by the Church Missionary Society in Nagasaki, and the American Mission Board at Yokohama.
Split into simpler sentences: Meanwhile, Americans tried diplomatic channels to legalize Christian missionary work. In 1869 two outposts had been established: by the Church Missionary Society in Nagasaki, and the American Mission Board at Yokohama.