the rain fall
Tractors
Arable land and metal ores.
Open farmland!
Open farmland!
Run-off, as caused by rain washing nutrients off farmland and into the rivers, can cause the water to become polluted and promote a choking abundance in the growth of algae and weed.
The existing central American population
Because it really didn't work. It basically punished the Central Powers and didn't settle any of the disputes between the nations that caused the tensions that exploded into war. And it created the completely useless League of Nations that wasted everyones time.
the thing that caused people to become interested in Alaska was the gold rush.
Traffic congestion.
Advanced economies
The North became an industrial powerhouse, and started to become more oriented toward compact cities on rivers instead of sprawling farmland. It also started created friction between the North and South due to the fact that their ways of life were so different.
Manifest destiny caused Oregon country to become a hot political issue.