Complex sentence: The Agency soon set up the Fort Berthold Reservation originally consisting of some 8 million acres (32,000 km²), but by 1910, the size of the reservation was about 900,000 acres (3,600 km²) of land.
Split into simpler sentences: The Agency soon set up the Fort Berthold Reservation, originally consisting of some 8 million acres (32,000 km²). By 1910, the size of the reservation had been reduced to about 900,000 acres (3,600 km²) of land.