Israel invades the gaza strip.

The Jews did not "come with the military intention of taking over Israel".

Jews had been trickling into this area since the 19th century. They built towns and agricultural communities and settled in to live. (Tel Aviv, for example, was established in 1909. The first Kibbutz, Dgania, was established in 1910). After the Turks lost WWI, the Jews started lobbying with the British for independence. The Arabs lobbied for Jews to not be allowed into Palestine. The British initially accepted the Jewish viewpoint (http://en.wikipedia.org/wiki/Balfour_Declaration), but later agreed with the Arabs, and forbade Jews to come here. Before, during, and after WWII, Jews were not allowed to immigrate to Palestine, but continued coming illegally. Once the British went anti-Zionist, the Jews set up underground/terrorist organizations to oust them. These organizations attacked the British military, not the Arabs.

In 1948 there were about 650,000 Jews and a million Arabs in Palestine. When the British finally left, without leaving the figurative keys to either side, the Jews declared their independence, and the Arabs - including both the local ones and the surrounding countries - launched an offensive against the Jewish towns and other communities. As stated before, they lost.
The Jews did not have tanks and planes, as they had been arming themselves as underground/resistance/guerrilla do. They did not come from outside to take over by force, they were protecting their towns and kibbutzim and wherever they were already living.

As for why Hamas exists: it exists because people were forced to live in refugee camps for decades. If the Arabs had taken their brothers in, back in 1948, or a few years later, the conflict might have continued, but this level of desperation and hatred would never have evolved. If they had been willing to accept any kind of peaceful compromise, instead of insisting on all the Jews "going back to Europe", everyone would have been happier. But no, it had to be all or nothing. And 60 years of nothing does take its toll on people's sanity. That's why Hamas exists and why the population of Gaza voted Hamas into power.

Seems like both of us are underestimating the side we're arguing against.

The Jews definitely had tanks and planes. They were definitely not guerillas. If you were told they didn't, I'm sorry, you've been misinformed.

I conveniently (curse you memory!) "forgot" the Arabs launched the initiave. You're right. I'll admit I was wrong in that aspect. After the initial offense though, the Jewish military did not just defend their homes though. They went, way, way, past the U.N. paritition line of 1947. Which is what my memory has been arguing for.