Complex sentence: In 1870, the First Vatican Council declared the dogma of papal infallibility and the Kingdom of Italy annexed the city of Rome, the last portion of the Papal States to be incorporated into the new nation.
Split into simpler sentences: In 1870, the First Vatican Council declared the dogma of papal infallibility. Also in 1870, the Kingdom of Italy annexed the city of Rome, the last portion of the Papal States to be incorporated in the new nation.