Another interesting museum !
I found a war where Romania was the attacker; the Second Balkan War in 1913, when Romania attacked Bulgaria in support of Greece and Serbia. Got to within about 10km of Sofia, and gained a decent amount of land in the subsequent Treaty of Bucharest. I'm not sure about WW2; Romania provided auxiliary forces for Germany going into Russia, but didn't really have a lot of choice. But yeah, that's about it; everything else seems to have been defensive.
1910s was very interesting decade in that part of the world. In 1912, during First Balkan War, Greece and Bulgaria fought against Ottoman Turkey. In 1913, during Second Balkan War, Greece and Ottoman Turkey were allies against Bulgaria. From 1916 to 1918, during First World War, Ottoman Turkey and Bulgaria were allies against Greece.