Gaza city is not even in the top 85(a). In fact, there are many cities that are denser than Gaza. For example, London, Cairo and New York.
2. Gaza is occupied by Israel:
Gaza has been 100% cleansed of Jews in 2005. In the same year, Israel also formally declared an end to Israeli military occupation of the Gaza Strip. Presently, There isn't a single Israeli soldier on Gazan soil. Israel doesn't fully control Gaza's borders either, since the strip has a Southern border with the sovereign state of Egypt. The latter fully controls at least one crossing, but chooses to keep it closed for their own political and economic reasons.
3. Gaza is one of the poorest regions in the world:
Gaza Strip's Human Development Index is usually around the 100th in the world (out of 177) (b). Higher than Egypt or Syria, but lower than the Palestinian average.
Life expectancy in Gaza is around 107th in the world, higher in fact than Glasgow (SNP likes to flaunt this). The Palestinians are the largest per capita recipients of foreign aid in the world and the 8th fattest nation in the world. By all global accounts, Palestinians are neither rich, nor poor, but strongly in the middle.
(a) WikiPedia - List of cities proper by population
(b) WikiPedia - Human Development Index