I know this is a difficult question, but I would like to point out a few facts. All of the area of Palestine had fallen into the territory of the Ottoman Empire until its collapse at the end of World War I when the territory that is now modern day Israel became a part of British mandate of Palestine. Jordan, Syria, and Lebanon were also created as European Mandates at this time. At the end of World War II the United Nations divided the Palestinian mandate between the Jews and the Arabs. The angry Arab nations refused to recognize Israel and invaded in 1948. Jordan, Syria and Lebanon also became independent nations at that time. None of them had been independent nations since medieval times or earlier.
From these facts, I do not believe the Israeli war for Independence was an agression. They were the ones invaded, not invading. Jews had lived in the area as settlers since the 19th century and had made great improvements to the land. The horrors of World War II inspired the United Nations to give them a homeland in this land. Arab inhabitants of the land were never told they had to leave and as pointed out earlier, were offered a home in Jordan so they did not have to become refugees.
My information comes from Jerry Speilvogel: Western Civilization. Fifth edition; Wadworth/Thomas Learning, 2003, 811-813.
I'm not qualified to answer your question other than to give my own opinion on the matter. However, I can give you some factual information on the Arab "refugees." When the nation of Israel was established, the King of Jordan offered a homeland to all of the displaced Arabs, and all Palestinians automatically became citizens of Jordan. They didn't have to end up like they are now. They could have established new homes and new lives in Jordan. Maybe it's understandable that they didn't want to leave their birthplace, but they didn't have to become "refugees" either.
Visit the sites linked below for more information.
Not really, it was the Arabs who started the conflict, since there was resentment among the Arabs as they did not recognise Israel's existence and independence as an own state, so they waged a war against the Israelites. They were angered by UN's decision of recognising a Jewish state, so started a war, so Israel's war of independence was not a form of aggression but as some sort of self-defence, a personal protection against invaders. It was not Israel, but the partition plan put forward by UN which allowed the Jews to have 56% of the territory that was the root cause of the conflict
As for the Arab refugee problem, It was not Israel's fault. The Arabs were giving an opportunity to build homes and live in their new homeland, around Jordan as approved by the Israel's government but they still choose to leave this country, becoming "refugees of war". I still think they have some grievance against Jews and did not want to stay in a land filled with their nemesises.
It really depends on who you ask, which perspective you take. The Israeli side points to the UN Partition which authorized two states, one a home for the Jews with an Arab minority, the other an Arab state with a Jewish minority. The Palestinians will point to the fact the battles started before the UN partition was announced, and that they didn't have much of a say regarding the borders, and that the UN plan made no mention of how existing Palestinian towns and villages would be compensated, etc. if they fell under Israeli control.
As for the refugee problem, it also depends on who you ask. Many villages were emptied out in contravention of UN rules, and many Arabs fled their homes in fear, assuming that they would be allowed back once the fighting was over, which they were not.
The following links can add some context.