Social stigma and repression of left-handedness
Many European languages (including English) use the same word for "right" (in a directional sense) to mean "correct, proper". Throughout history, being left-handed was considered as negative - the Latin and Italian word sinistra (from which the English 'sinister' was derived) means "left". There are many negative connotations associated with the word "left-handed": clumsy, awkward, unlucky, insincere, sinister, malicious, and so on. French gauche, meaning "left", means "awkward or clumsy" in English, whereas French droit is cognate with English "adroit", meaning dexterous, skillful with the hands. As these are all very old words, they would tend to support theories indicating that the predominance of right-handedness is an extremely old phenomenon.
The Eskimos believed that every lefty was a sorcerer. A Japanese man could divorce his wife if he discovered that she was left-handed. There have been, however, many famous left-handed people, and the associated right brain hemisphere that is said to be more active in left-handed people has been found in some circumstances to be associated with genius and is correlated with artistic and visual skill.
Until very recently in Taiwan, left-handed people were strongly encouraged to switch to being right-handed (or at least, switch to writing with the right hand). It is more difficult to write legible Chinese characters with the left hand than it is to write Latin letters. Remember that "easy" and "difficult" depend on the person using those terms, so your writing may be neater. Because it is supposedly easier to write when moving your hand towards its side of the body, it is easier to write the Roman alphabet with your right hand than with your left. Conversely, Arabic and Hebrew, which go from right to left, would be easier to write with the left hand. Again, "easier" and "harder" are subjective.
Until the latter part of the twentieth century, Roman Catholic nuns in American elementary schools (and possibly elsewhere) would punish children for using their left hand to write, typically by slapping their left hand with a ruler if they attempted to pick up a pen with it. Left-handedness was interpreted as a sign of Satanic influence, and thus prohibited.
It has been hypothesized that some sun worshipers have grown to associate their left sides with evil, since people facing north would see the sun set (disappear) on their left. The evidence for this is very weak, however, as the opposite conclusion can be drawn when one considers a person facing south (the opposite direction). It has been suggested that there may be a preference for northern hemisphere dwellers to face the fixed north star (i.e., north) when making directions judgments.