Complex sentence: In the 1922 reorganisation of the British Indian Army the four Sikh regiments became the first four battalions of the newly-constituted 12th Frontier Force Regiment whilst the infantry element of the Corps of Guides became its 5th and 10th (training) battalions.
Split into simpler sentences: In the 1922 reorganisation of the British Indian Army the four Sikh regiments became the first four battalions of the newly-constituted 12th Frontier Force Regiment. The two infantry battalions of the Corps of Guides became its 5th and 10th (training) battalions.