Complex sentence: Upon the outbreak of war, the 4th Guards Cavalry Brigade was dissolved and its component regiments were assigned as divisional cavalry to the 1st Guards Infantry Division (Life Guard Hussars) and 2nd Guards Infantry Division (2nd Guard Uhlans).
Split into simpler sentences: Upon the outbreak of war, the 4th Guards Cavalry Brigade was dissolved. Its component regiments were assigned as divisional cavalry to the 1st Guards Infantry Division (Life Guard Hussars) and 2nd Guards Infantry Division (2nd Guard Uhlans).