Polygyny
As with other animals that have strong patriarchal hierarchies, some human societies practice polygyny: a man having multiple female mates as a culturally-acceptable arrangement. Historically, polygyny has been most common in agrarian societies, where a large labor force is favorable. In the United States, Mormons practiced polygyny with church sanction until 1890, when it was prohibited by the church, having already been outlawed under federal statute. (Lecherous Mormon church founder Joseph Smith had ~40 wives, including marrying one who was only 14 at the time.)
Muslim men in several countries still practice polygyny. Polygyny remains legal in Saudi Arabia, Iran, Afghanistan, Pakistan, the Philippines, Singapore, Malaysia, and most north African nations. In other Islamic countries polygyny is restricted or banned, albeit still practiced illegally. Polygyny is practiced throughout much of Africa.
Men hoarding wives leaves less-fortunate men without mates. Unsurprisingly, polygynous societies are bloodier, more likely to invade their neighbors, and more prone to collapse. Polygyny features in all of the 20 most unstable countries in the world.
