According to my own knowledge , when the economics began to slow down e.g. In the Great Depression , countries began to send tariffs and quotas to other countries . This makes local food/goods seem cheaper than food/goods imported from other countries , so ppl. will tend to buy/consume local food/goods instead of those imported food/goods . Also , if countries send high tariffs and quotas to other countries , this might lower their initiative to export food/goods too . This will therefore protect those local homr markets .