Complex sentence: Only two weeks after the Italian declaration of war, the Second Armistice at Compiègne ended British access to French Mediterranean Sea bases; and the 3 July 1940 attack on Mers-el-Kébir hardened French antipathy towards Britain.
Split into simpler sentences: Only two weeks after the Italian declaration of war, the Second Armistice at Compiègne ended British access to French Mediterranean Sea bases. The attack on Mers-el-Kébir (3 July 1940) hardened French antipathy towards Britain.