Israel invaded? How strange, I always thought it was the
other way around, especially considering that, as of these wars, Israel had been formed out of most of Palestine (Note that, under the British mandate system, the region was split into Trans-Jordan and Palestine, most of the latter would later be incorporated into Israel and the remainder to the Arabic Muslims).
Now, if you're talking about the Sinai War or the Six Days War, the former was triggered by Israeli fears of another invasion after the closing of the Suez Canal to all Israeli traffic (Thus seriously debilitating their economy...EDIT: Almost forgot, also it was in violation of the UN SecCouncil Resolution signed 1/10/1951), the signing of an alliance between Egypt, Jordan, and Syria, effectively surrounding Israel with a cohesive hostile alliance, and the rapid militarization of the Sinai. Israel, understandably, decided that this was directed against them (Surprise, surprise), and decided to act to prevent their country from being swamped a second time by invading before their enemies were ready. Even so, after crushing the enemy, they withdrew and turned the spoils of war over to the UN (And indirectly, back to the original owners), rather than keeping it for themselves. So it seemed from this action, I would say they didn't want to expand, but rather they wanted a safe buffer from proven hostile powers.
The Six Days War, again, was started when Egypt kicked out the UN forces, mobilized their forces in the Sinai, and closed the Gulf of Aqaba to Israeli shipping again, while Syria and Jordan also moved in various border incidents and, in the former case, active support of Palestinian insurgents (Or, since it's just as valid if from a different POV, freedom fighters). Again, Israel decided that these actions were being taken as a prelude to another assault (Why else would you prepare your armies, damage another country's economy, probe their defenses, and try to trigger infighting behind the front lines?), and launched another preemptive assault, with just as much success as the last. This time, considering the failure of the UN last time, they kept the land, but would later return the Sinai to Egypt after relations normalized between the two countries.