Such agreements have been in place formally or informally throughout much of mankind's history. Before Europeans settled in North America, Aboriginal peoples often entered into agreements with each other about their territories and to protect each other from a more powerful group. During the War of 1812, the Americans were angry because they believed that the British had aligned themselves with the First Nations to help them in their battles against the Americans.

You may have heard the term military alliance before. A military alliance is an agreement between two or more countries to work together to protect each other from attack. Military alliances have been around for a very long time. One of the earliest military alliances on record goes back over 700 years and was called the Auld Alliance. The Auld Alliance was between Scotland, France, and Norway and stated that if England attacked one of these countries, the others would invade England.
 
 Another common practice in earlier times was to form alliances with other nations through having members of royal families marry each other. It would be unlikely that a king of one nation would invade another's kingdom if his daughter was married to the other's son.

By the end of the 19th century, interaction among nations was far greater than in previous history. Several European nations had formed alliances as they attempted to secure their own territories from any threat from other nations. The growth in alliances began at the end of the 19th century when the German Empire and Austria-Hungary signed the Dual Alliance to try to combat the influence of Russia in the Balkans.

When Italy joined, this became the Triple Alliance. About 10 years later, France and Russia signed the Franco-Russian Alliance in response to the Triple Alliance. Within a few years, Britain joined to create the Triple Entente. Early in the 20th century, both of these alliances increased their influence in the area known as the Balkans, and by 1907, all of the main European powers were committed to the military support of each other through a series of treaties and alliances. Europe, divided into two main camps, was just waiting to explode. The assassination of the Austrian Archduke was the spark that ignited the hostilities that had been brewing for decades, and World War I began.