In May 1915, Italy attacked Austria–Hungary. Italy was the only military opponent of Austria–Hungary which had a similar degree of industrialization and economic level; moreover, her army was numerous (≈1,000,000 men were immediately fielded), but suffered from poor leadership, training and organization. Chief of Staff Luigi Cadorna marched his army towards the Isonzo river, hoping to seize Ljubljana, and to eventually threaten Vienna. However, the Royal Italian Army were halted on the river, where four battles took place over five months (23 June – 2 December 1915). The fight was extremely bloody and exhausting for both the contenders.