Slavic peoples migrated and settled throughout the 5th and 6th centuries, and created a semi-independent administrative region known as Duklja.
In 1042, Duklja became fully independent, and spent the following years expanding its territory. However, by 1186 there was a significant decline in power resulting in the loss of freedom, and this pushed the region into assimilating with the Serbian Empire.
Along with the Serbian Empire in the 16th century, and much of southeastern Europe, southwestern Asia and Northern Africa, Montenegro became part of the Ottoman Empire.
Despite the autonomy the country received from the Ottoman's, Montenegro evaded the rules put forth and attempted many revolts to regain their independence.
They were finally successful in their attempt in the 1800's under the rule of Nicholas I. During his reign, Montenegro emerged as a kingdom, and drafted its first constitution referred to as the Danilo Code.
During World War I, Montenegro formed an alliance with Serbia, and unfortunately for the two were overrun by the Central Powers. As Austria-Hungary occupied the region, King Nicholas escaped to France and controlled operations through Bordeaux.
Upon liberation by the Allies, King Nicholas was banned from returning to Montenegro, and the country was subsequently united with Serbia (despite the violation this caused with the constitution).
In the years leading up to World War II, the Slovenes, Croats and Serbs together formed the Kingdom of Yugoslavia, and as a part of Serbia, Montenegro was also lumped into the New Kingdom.