<span>It promoted the growth of plants, and thus early settlers began moving inward to warmer places in search for better land for cultivation.</span>
C) populism
For future reference: an easy way to remember the causes is to use the acronym MAIN (as in the MAIN causes) to remember that they are militarism, alliances, imperialism, and nationalism.
Hope this helps :)
The railroad increased commerce by making shipping easier and cheaper.
