Why did Italy fear that France would invaded them that lead them to join the alliance with Austria and Germany.

The treaty provided that Germany and Austria-Hungary were to assist Italy if it was attacked by France without provocation. In turn, Italy would assist Germany if attacked by France. In the event of a war between Austria-Hungary and Russia, Italy promised to remain neutral. The existence and membership of the treaty was well known, but its exact provisions were kept secret until 1919.