This diploma thesis presents the formation of the Ottoman principality and its evolution from a frontier principality to an empire. The main emphasis is on identifying the causes for the Ottomans’ successful development in relation to their neighbouring countries, notably Byzantium. The Byzantine decline in the same period of time is very important in order to understand the topic. Later, the Serbs played a major role due to being the greatest threat to the Ottomans, but they too succumbed to their pressure as a consequence of internal strife. This work also focuses on why the Ottomans chose to head more towards Europe rather than Asia. The answer is once again found in the fact that Europe offered better opportunities due to the poor state of its neighboring countries, while neighboring countries in Asia were in better condition to defend themselves against an Ottoman attack.