Why did Josiah strong write this. The perdominance of the Anglo Saxon race

Josiah Strong (1847 - 1916) was an American Protestant clergyman, leader of the Social Gospel movement. In his book The predominance of the Anglo Saxon Race, he called for Anglo-Saxons to spread their superior establishments and values to what he described as inferior races. Civilizing savage societies was believed to be a call from God in preparation for a future when the world's different races would compete for total domination.