What I have learned about their enemies
What I have learned about their enemies is that they didn't get attack that often they were mostly at peace. That gave them a lot of time to work on their defense. The northern part of Egypt was invaded by the Hyksos. They lost their capital as well.
I got the information from my google notes.
The old kingdom
There army was mostly made of farmers. They didn't have the supplies to train them.
Here is the creator
The sites that I used