What event caused increased the numbers of settlers in the west, the range of commerce and contributed to the growth of cities like chicago and denver?

Chicago  became a transportation and commercial center in 1850's. The extraordinary growth of the city in the 1850's was attributed to the rapid increase of railroads namely the Galena & Chicago Union Railroad and their effects which made transportation and trading of goods easier than the previous method of trading by steamboats. Moreover the direction of trade shifted from north-south to east-west.

The settlements in Denver increased in 1858 due to the Pike's Peak Gold Rush.This was the first historical settlement in the city of Denver.

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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.