This was a mixture of things.
The increase in population from soldiers and influx of immigrants caused the need for more food to be produced and more jobs to be demanded. So farmers started over producing which led to the Dust Bowl and, eventually, the Great Depression.
The best option in terms of El Nino would be "<span>the cyclical warming of the Pacific Ocean near the equator," since this weather event is "expected" practically at the same time every year. </span>
The answer is Oregon. This is solidified through the treaty called the Treaty of Oregon. In this treaty, the US and the British government had created a boundary to stop states to fight over their territories. The treaty had stated that Oregon county is a joint territory between the US and the British government.
