In WW1 The German invasion of Belgium resulted in a threat of widespread starvation as the country produced only 25% of it's food needs and was unable to import food. This triggered a huge relief program which allowed the US and other nations to send 5.7 million tons of food feeding 11,000,000 people mostly Belgian but also parts of occupied France and other nations. Herbert Hoover was able to arrange safe passage for the ships with agreements from France, Britain and Germany.

In WW2 the German invasion of Greece caused a similar food shortage. This time, however, the combatants were much less willing to cooperate. Britain managed to buy some food in Turkey and have it shipped on Turkish ships to Greece but corruption in Greece and price gouging in Turkey limited the effectiveness of this aid. British mistrust of Germany led to Britain ending the program with only 25% of their goal of 50,000 tons sent.

Sweden and the Red Cross managed to arrange a system where Swedish observers would ensure that Germany did not use the relief food. Throughout the war shipments were delayed or cancelled because of mistrust between the parties. As a result of this mistrust as many as 300,000 Greeks died.

Officially there were definitely agreements that were honored but in comparing CRB of WW1 and the relief efforts of WW2 shows a huge difference in how the combatants viewed each other.

For more information check out Famine and Death in Occupied Greece, 1941-1944 by Violetta Hionidou

Also check out this Great Article about the Commission for Relief in Belgium