Complex sentence: In 1816 he went back to Buenos Aires, but the new Supreme Director, Juan Martín de Pueyrredón, forced him to return to exile in San Juan wheree he helped José de San Martín organize the Army of the Andes for the crossing into Chile.
Split into simpler sentences: In 1816 he went back to Buenos Aires, but the new Supreme Director, Juan Martín de Pueyrredón, forced him to return to exile in San Juan. Thee he helped José de San Martín organize the Army of the Andes for the crossing into Chile.