related resource TeachforSDGs.com No one reason but
1962 EU common agricultural policy ended its defining purpose (Messina 1955) of peace to all - it restarted the corn laws that the economist in 1850s with Queen Victoria had got the british empire to repeal. The British repeal had come too late to stop about a seventh of Irish people from starving. Setting monopoly prices and supply in the richest part of the old world. The EU prevented former colonies from developing their agricultural economies optimally
The EU policy also spiraled problems at any to the EU - on way of selectively including new countries which were developed enough to join in