Complex sentence: He studied at the Lycée de Bruges and then at the Lycée Louis-le-Grand in Paris and after participating in the defense of Paris in 1814, he attends the École Polytechnique in 1815.
Split into simpler sentences: He studied at the Lycée de Bruges and then at the Lycée Louis-le-Grand in Paris. After participating in the defense of Paris in 1814, he attended the École Polytechnique in 1815.