Wasn´t it overcrowded from the 1948-war, when it was filled with refugees from the area that was to become Israel?
What does "overcrowded" mean?
It's very difficult to say the exact population of the Gaza Strip before partition because it wasn't any kind of subdivision. There was a subdivision that included all of the Gaza Strip, but it also included a bit more, including further up along the coast past what is today Ashdod and a little bit further inland. A UN report from 1946 indicates that this area has a little more than 100,000 people; I've seen estimates that the population of the what would be the Gaza Strip was probably about 80,000. This rose to over 300,000 by 1950.
But what does overcrowded mean? So before, we're looking at a population density of say 200-220 people per square kilometer, similar to modern Germany or the Dominican Republic, and after of between 850 and 900 people per square kilometer, similar to modern Bangladesh (precise numbers for the population are hard to find). Note that Bangladesh is the densest non-city-state in the world. So certainly the Gaza Strip after 1949 was very crowded, but I don't know that it was overcrowded,
per se. Certainly it wasn't able to feed itself, and infrastructure was terrible, but that's more a product of enormous population inflow rather than necessarily being an unsustainable level. With intense agriculture, Gaza could probably have fed itself, though obviously it didn't have the money or expertise to implement that. Probably the consumption at an unsustainable rate of water from the aquifer began around that time, though considering the relatively low rainfall and lack of major rivers to the area, it's actually very possible that use was unsustainable even before the massive spike from the displaced population.
I actually think I've convinced myself that overcrowded is a good word to use.