Complex sentence: However, in 1898 as the war with Spain began, a three-battalion, 12-company structure was effected, proportionally the same roughly approximate size as the single battalion, ten-company regiments of the Civil War.
Split into simpler sentences: However, in 1898 as the war with Spain began, a three-battalion, 12-company structure was effected. This expanded regimental structure produced units, proportionally the roughly the same approximate size as the single battalion, ten-company regiments of the Civil War.