British trade decreased after world war i because

Because much expenditure was used during WWI,for the operations, weapons, and resources, and a lot of capital is needed for rebuilding the destroyed of infrastructure, Britain decreased trade ro secure her own economy.
Due to the fact that increased trading would cause instability of economy that the government might not be able to handle.
Thus closing off the tradings was to secure herself.

Hope it helps!

They said that the world was flat