Why was Rationing introduced!?

Tray_containing_a_ration_book_and_the_weekly_ration_of_sugar,_tea,_margarine,_'national_butter',_lard,_eggs,_bacon_and_cheese_as_issued_to_an_adult_in_Britain_during_1942._D79
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Rationing was introduced in WWII because the government did not want the civilians to starve to death, as the Germans were bombing all the boats that imported foods from other countries.

This is a tray containing a weekly ration.