What event opened the northwest territory to american expansion?

The Treaty of Greenville opened the northwest territory to American expansion.

This treaty was signed between the United States and Indians of the Northwest Territory in 1795. It was signed at Fort Greenville in order to set the boundary between Indian lands and Whiteman's lands in the Northwest Territory which is currently known as Midwest including states like Ohio, Michigan, Indiana, Illinois, Wisconsin and Minnesota.

the graph shows the spread of railways in the 1800s.

based on the graph, the conclusion that can be drawn about germany is answer d)   by 1880, germany had more rail lines than great britain and russia.