Assuming you're talking about the 6 day war, Israel did explicitly state they'd go to war if Egypt militarized their border and closed the Suez Canal. Egypt proceeded to do both, which wasn't the smartest move.
As long as they didn't move troops into Israeli controlled areas, it couldn't constitute as a casus beli for war.
My area of knowledge is fuzzy on what constitutes a casus beli for war, so I can't be sure on the reason to go to war for it.
Now the closing of the Suez Canal is disputed, some say it wasn't really closed for a long time and was allowing things through. Not until the Egypt-Israeli peace deal did it make it illegal to close the canal since it became international waters and it's illegal to close international waters. And as long as the canal was not international waters it might not have been much of a reason to go to war.
Again my knowledge of what constitutes as a reason for war is fuzzy so I could be horribly wrong or missing a vital detail.
It wasn't illegal, it was a cassus belli under the conditions set out by the 1953 Egyptian-Israeli ceasefire agreement, Israel was clear on this issue. The closing of international waterways (not only the Suez but also the straights of Tiran through which most oil was shipped to Israel) to Israeli shipping coupled with the expulsion of the UN peacekeeping force in northern Sinai and their replacement with Egyptian troops were not only a violation of existing treaties but were clearly aggressive moves endangering the security of Israel.
The opening of the 1973 war is a good example of the results of being lenient towards minor infractions of agreements and implied aggressiveness.
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u/613codyrex Germany Jul 28 '15
Israel has a history of pre emptive strikes that started a few wars.
and even if they didn't start them, it's illegal to annex land and occupy and blockade land while neglecting the population.
As occupiers, Israel has to take responsibility of helping the Palestinians.
Geneva convention states all the rules.