Answer:
The Ancient Egyptian empire became diluted in 525BC when Cambyses II of Persia defeated Psammeticus III, who was the last Pharaoh of the 26th dynasty. It continued under Persian rule until 332BC when Alexander the Great defeated the Perisans, and instituted the Ptolmeic Dynasty which saw Egypt come under Greek rule. Following on from this the Romans' conquest of 30BC by Octavian, saw Egypt come under Roman rule as the Roman provice of Aegyptus. During these periods; although the Administration of the country changed the Ancient Egyptians were allowed to worship their own gods. Ptolomey even styled himself as a Pharoh. It was not until the begining of the first century AD, that civil conflict epupted between the Greeks, Jews, and Christians (caused by the rapid spread of Christianity) ultimatley Christianity won through, as older paganistic religions were suppresed as 'Evil' so monuments, and temples were ransacked, This effectivley constituted the death of the "Ancient Egyptian Empire".
Have a look at this blog. It seems pretty new but has lots of good information about the history of the Egyptian empire and is updated reguarly
ancient-civilisations.blogspot.com