C. Using government spending to stimulate the American economy.
It was a bad decision on his part. Some may say his decision was good at the beginning but ultimately he made the choice to stay at war which led to a bad turn of events. Millions of dollars were spent on this and it wasn't even really successful, so I believe that was a poor decision.
They weren't so successful at conquering Europe or China. Of course, one can blame the long supply lines, but in these cases their adversaries were also determined to repulse them.
In contrast, Byzantium and Persia were exhausted from mutual warfare. Tribes related by kinship to Muslim Arabs had served as mercenaries during this period, so there was a lot of tactical knowledge available.
The Byzantines retreated to the highlands of Anatolia upon losing their lower-lying provinces to the Muslims. I am not sure if they launched a determined counter-attack. The Persians did, but they could not fight coherently.
