A trade war is an economic conflict often resulting from extreme protectionism in which states raise or create tariffs or other trade barriers against each other in response to trade barriers created by the other party. If tariffs are the exclusive mechanism, then such conflicts are known as customs wars, toll wars, or tariff wars; as a reprisal, the latter state may also increase the tariffs. Trade war arises only if the competitive protection between states is of the same type and it is not valid in case of dumping exports (Perju, 2009). Increased protection causes both nations' output compositions to move towards their autarky position. Minor trade disagreements are often called trade disputes when the war metaphor is hyperbolic.

Trade wars could be escalated to full conflict between states, as evidenced in the Massacre of the Bandanese after alleged violations of a new treaty. The First Anglo-Dutch War caused by disputes over trade, the war began with English attacks on Dutch merchant shipping, but expanded to vast fleet actions. The Second Anglo-Dutch War for control over the seas and trade routes, where England tried to end the Dutch domination of world trade during a period of intense European commercial rivalry. The Fourth Anglo-Dutch War over British and Dutch disagreements on the legality and conduct of Dutch trade with Britain's enemies in that war. The Shimonoseki Campaign after unrest over the shogunate's open-door policy to foreign trade. The First Opium War which started after the Qing government blockaded its ports, confiscated opium contraband and confined British traders, resulted in the dispatch of the British Navy to China and engage the Chinese Navy in the Battle of Kowloon. The First Opium War eventually led to the British colony of Hong Kong, and the Second Opium War, which arose from another trade war with the same underlying causes, expanded the British possessions on the island.