For many reasons, but basically it comes down to these two:
1. Pacifist German Mennonites moved to Russia with promises from
Catherine the Great in 1763 of land, religious freedom and
exemption from being force to fight in wars. These exemptions were
dropped in 1870 and peace loving Mennonites were forced into
military service for Russian or imprisonment. Between 1874 and
1880, of the approximately 45,000 Mennonites in South Russia, ten
thousand departed for the United States and eight thousand for
Manitoba.
2. Meanwhile in the US the Civil War had just ended and the west
was being opened up to settlers by the railroads. These railroad
companies had been granted by the US Congress, large amounts of
land along side these rail lines. So these companies sent their
representatives to Russia to offer land to farmers willing to
settle in the US Midwest. The railroad company that was most
successful in recruiting these Mennonites was the Santa Fe Railroad
(now part of the BNSF railroad), because they sent some Mennonites
to help persuade these Russian Mennonite farmers to move. Many of
these Mennonites settled in the state of Kansas, along with South
Dakota, and Nebraska.
