In the 16th century, the demand for African slaves by European colonial powers increased as England and Spain officially legalized international slave trade. One effect of this in West Africa was the expansion of warfare. Some local leaders, viewing the slave trade as an opportunity for profit, began engaging in constant warfare with neighboring groups in order to take captives to sell to European traders. A few West African states developed a thriving economy due to constantly taking prisoners of war from nearby states. Additionally, these leaders sometimes used the profit from selling war prisoners to buy guns and other weapons from European traders, which facilitated their ability to engage in constant war. Ultimately, the economic advantage experienced by some West African leaders was short-lived, as the slave trade devastated local populations and eventually the economy of all of West Africa.