Complex sentence: Langenau, the quartermaster-general of the Grand Army, found him an indispensable assistant, and he had a considerable share in planning the Leipzig campaign and as a tactician won great praises in the battles of Brienne and Arcis sur Aube.
Split into simpler sentences: Langenau, the quartermaster-general of the Grand Army, found him an indispensable assistant, and he had a considerable share in planning the Leipzig campaign. As a tactician he won praise in the battles of Brienne and Arcis sur Aube.