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.
The Black Death is believed to have been the result of plague, an infectious fever caused by the bacterium Yersinia pestis. The disease was likely transmitted from rodents to humans by the bite of infected fleas.
FOMC sets a target federal funds rate eight times a year, based on prevailing economic conditions. The federal funds rate can influence short-term rates on consumer loans and credit cards as well as impact the stock market.
