I am researching the Balkans involvement in World War 1. Specifically, Bulgaria, Serbia, and Romania.

What I know so far is that Bulgaria lost the Second Balkan War to Serbia, Greece, and Romania. This induced pre war tensions between the Balkan country's,regarding territory disputes over many areas including Thrace, and North Macedonia. The larger empires also played separate roles in pre war and war tensions, such as Russia, Austria Hungary, and the Ottoman Empire.

Russia in that time (1913), had Balkan allies, including Serbia and Bulgaria, which Russia considered valuable assets.

The Ottoman Empire, during the Second Balkan War, played its hand, to try and regain territory lost in the first Balkan War. Austria Hungary, was sided with Romania, at the end of the war - signing an agreement with Italy to have the recently independent country of Albania, lose its independence.

The cause of World War 1 is greatly contributed to the assassination of the Archduke of Austria-Hungary by the Serbian group of Black Hand. However, the Balkan Wars, and tension of many alliances in Europe were causing such feuding, that grew out of control when the Archduke was killed.

Balkan Countries such as Bulgaria and Romania did not join the First World War, until October, 1915 (Bulgaria) and 1916 (Romania). Bulgaria was at the time, growing apart from Russia, which may have helped decide why they joined the Central Powers. However, it is strange that Bulgaria joined Central Powers, because one of their long time enemies was the Ottoman Empire - who they fought historically, and in the First Balkan War.

Other tensions include: the series of 12 wars between Russia and the Ottoman Empire, called the Russo Turkish wars. Also, as I included before, Bulgaria was feeling neglected from their ally, Russia, accusing them of meddling in internal affairs and favoring Serbia. Also, even before the Archduke assassination, Serbia was unhappy because Austria-Hungary and the British Empire limited Serbia's territory after the First Balkan War.

My question is: What were Romanian - and Bulgarian relations in, and around the lead-up to the First World War, and the War itself. Also, what made Bulgaria decide to fight the Second Balkan War - as they were the ones who made the first move. And, finally, what was the relation of the Great European Powers, and the Balkans within the 1900 - 1920 (why did they consider the Balkans valuable, and what did they do about it).