Complex sentence: In accordance with Eastern Force Order No.53 Previously, the two existing divisions (ANZAC Mounted Division and Imperial Mounted Division) each contained four mounted brigades; hereafter, the three divisions would have three mounted brigades each.
Split into simpler sentences: In accordance with Eastern Force Order No.53 Previously, the two existing divisions (ANZAC Mounted Division and Imperial Mounted Division) each contained four mounted brigades. Hereafter, the three divisions would have three mounted brigades each.