In early civilizations, food shortages would have been very common. There were a number of reasons for this. Let us look at three of them.
Lack of production. In this time before there was much technology, farmers could not grow that much food. They were also much more susceptible to crop failure from disease, insects, or weather. This meant that shortages were common.
Lack of storage. Most kinds of foods could not readily be stored during this period. Therefore, it was hard to build up a surplus that could be used to prevent shortages.
Inability to transport. Land transportation was practically nonexistent. Therefore, one area could experience food shortages when another relatively close area could have plenty of food but be unable to share.