Complex sentence: The 1/1st Shropshire Yeomanry was part of the Welsh Border Mounted Brigade, which in 1914 was attached to the 1st Mounted Division., then in 1915 they were dismounted and served in the Western Desert as part of the 4th Dismounted Brigade in Egypt and Palestine.
Split into simpler sentences: The 1/1st Shropshire Yeomanry was part of the Welsh Border Mounted Brigade, which in 1914 was attached to the 1st Mounted Division. Then in 1915 they were dismounted and served in the Western Desert as part of the 4th Dismounted Brigade in Egypt and Palestine.