Several factors came together. Europe had a population that was on average richer than most other cultures. A very competitive commercial class, ships that were superior than other cultures, developed for the rough North Atlantic, and a number of competitive states rather than a single empire.
The major physical feature that the pioneers crossing West had to contend with were the Rocky and Sierra Nevada Mountains.
These mountain ranges were treacherous and many died trying to find passages to cross.
A would be correct. The US employed “island hopping” or “leapfrogging” tactics as a way to quickly move across the Pacific toward Japan. A small landing force could decimate a Japanese stronghold and replace it with an American base from which another landing force would launch. It cut back on cost and time, since a fleet wouldn’t have to return to a base thousands of miles away to refuel and regroup any longer.
