Complex sentence: Kilts have been traditionaly worn without undergarments since its use as part of Scottish military uniform, leading to the invention of such expressions as "go regimental" or "military practice" for wearing no underwear.
Split into simpler sentences: Kilts have been traditionaly worn without undergarments since its use as part of scottish military uniform. This let to the invention of such expressions as "go regimental" or "military practice" for wearing no underwear.