Lack of several critical material resources, particularly iron and straight timber, caused Egypt to import these items using wealth from its natural resources of gold, and control of the Africa-Asia trade routes. Regular conflicts with the Hittite Empire and the Assyrians for control of the Levant (modern-day Syria, Lebannon, Israel, Palestine, and Jordan) sapped Egypt's military resources. Over time, Egypt became weakened both within and without. It succumbed to invasion by the Kushites in the 7th century BCE, and then fell to the Second Babylonian Empire in the 6th century BCE. The Persians added Egypt to their empire in the 5th century BCE, Alexander the Great conquered Egypt in the 3rd century BCE, and then Julius Caesar and Octavian Augustus Caesar annexed Egypt for the Roman Empire in the 1st century BCE. It would not achieve independence from outside forces until the 7th century CE.