Greece is a mountainous peninsula, mountains cover ¾ of Greece.There are approximately 1400 islands in the Adriatic, Ionian, and Aegean Seas.Although fertile valleys cover one quarter of the peninsula, only about 20% is suitable for farming, Greek diet consists of grains, grapes, olives. Lack of resources most likely led to Greek colonization. Mycenaeance was one of the first people in ancient Greece.around 1200 BCE the mysterious “sea people” began to invade Mycenae, and burnt palace after palace. So, the Dorians moved into this war-torn region. Dorians were far less advanced. The trade-based economy collapsed. Writing disappeared for 400 years.