Complex sentence: In 1834 President Antonio Lopez de Santa Anna had been taking measures against federalism towards a more centralized system, that politicians in Zacatecas looked askance, as these were supporters and defenders of this system since its implementation in 1824.
Split into simpler sentences: In 1834 President Antonio Lopez de Santa Anna had been taking measures against federalism towards a more centralized system. Politicians in Zacatecas looked askance, as they were supporters and defenders of the existing system since its implementation in 1824.