What environmental factors helped with development of North America?
This depends to some degree on what you would call an "environmental factor."
If geography and topography are environmental factors, we can say that things like the presence of the Great Plains and the presence of gold in California helped develop North America. The Great Plains could be farmed and it was relatively easy to run railroads across them. The presence of gold in California encouraged westward expansion and enriched the country. The existence of the Mississippi River system also helped by allowing water transport of goods in that very large region.
If we are talking about climate, one factor was the fact that the Great Plains experienced relatively wet years in the time after the Civil War. This helped to induce whites to settle in the region. The settlement of the plains helped to drive westward expansion.