original: He stayed there until the outbreak of the Franco-Prussian war in 1870, when he became an army chef.
simplifications: He stayed there until the start of the Franco-Prussian war in 1870. He than became an army chief. He stayed until the Franco-Prussian war, when he became an army chef. He stayed there until the start of the Franco-Prussian war in 1870. He became an army chef. He stayed there until the the Franco-Prussian war began in 1870. At that time, he became an army chef. He stayed there until the Franco-Prussian war in 1870, when he became an army chef. He remained there until the outbreak of the Franco-Prussian war in 1870, he then became an army chef. He stayed there until the outbreak of the Franco-Prussian war in 1870. This was when he became an army chef. He stayed there until the start of the Franco-Prussian war in 1870. Then, he became an army chef. He stayed there until the onset of the Franco-Prussian war in 1870.  Also,  In 1870  he became an army chef. He remained there until the outbreak of the Franco-Prussian war in 1870, when he became an army chief.