Complex sentence: Although he was offered the Secretaryship of War in the Administration of President George Washington, he declined it, as well as a 1798 commission to Brigadier General during the preparations for the coming Quasi-War with France.
Split into simpler sentences: Although he was offered an appointment as the Secretary of War in the administration of President George Washington, he declined it. Similarly, he decline a 1798 commission as Brigadier General during the preparations for the coming Quasi-War with France.