Complex sentence: On November 11,1880 the congregational missionaries began to evangelize the highlands in Angola, this was the American Board of Foreign Missions (now it's the United Church of Christ in the USA) and the Congregational Church in Canada joint effort.
Split into simpler sentences: On November 11,1880, the congregational missionaries began to evangelize the highlands in Angola. This was the American Board of Foreign Missions (now it's the United Church of Christ in the USA) and the Congregational Church in Canada joint effort.