Complex sentence: The were a class of four warships built initially for the Imperial Japanese Navy (IJN) as light cruisers in the early 1930s under the weight and armament restrictions of the London Naval Treaty.
Split into simpler sentences: The were a quarter of cruisers built for the Imperial Japanese Navy (IJN) during the 1930s. They were initially classified as light cruisers under the weight and armament restrictions of the London Naval Treaty.