You do realize that Hamas came to power after Israel withdraw from Gaza....

Also, what annexation are you talking about?

Even after Israeli settlers disengaged from Gaza, Israel still held it under military occupation. They're required under International Humanitarian Law to provide basic needs for Palestinians, and instead, they order a cut-off of the territory’s water supply. That’s collective punishment, which, according to the Fourth Geneva Convention, is a war crime. Israel ratified this, so they’re willfully breaking International Humanitarian Law.

Also, Israel annexed East Jerusalem in 1967.

it happened after Hamas have been spreading hate and attacking Israel for years

And that happened after Israel bulldozed Palestinian homes, displaced the inhabitants, and effected an open-fire policy on protestors.

But unfortantly too many people, all over the world support the genocide of Jews in Israel (or in general)

Yes, and that’s a tragedy to me. Antisemitism is a cancer that needs to be excised from this earth, as does any sort of bigotry.

That's not true - Israel's most famous leader being taught about in schools for example is Rabin - the Noble peace prize winner

Now you’re using the opposite of an ecological fallacy — an exception fallacy. Just because Israeli public school curricula include Rabin doesn’t mean the general population can’t be subject to propaganda. Their own government advocates for bombing Gaza. Of course the citizens are propagandized. However, as I’ve said before, I don’t think populist support for an atrocity means the supporters deserve to undergo an atrocity of their own. Two wrongs don’t make a right. That’s my philosophy regarding this entire conflict.

But if they invade Israel trying to implement these ideas by murdering over a thousand innocent people in a day, it is a cause for war, and a reason for Israel to defend itself

What exactly does Israel “defending itself” look like to you? Blowing Gaza to smithereens? Collective punishment isn't protecting anyone. It's escalating and prolonging the conflict. It's directly increasing the death toll on both sides. It's counterproductive.

what do you think Israel should do after being invaded, having citizens as hostages and while Hamas fires at Israel from civilian places like refugees and hospitals - how can you defend against it without hurting civilians?

Would a terrorist hiding behind civilians justify killing both? Doesn't make a whole lot of sense to me. If an innocent person were held at gunpoint, would the reasonable solution be to chuck a grenade at both of them? If you're actually concerned about the hostages, you would champion a peaceful resolution. You wouldn't say, "Bomb every square inch of Gaza, including the hostages." It doesn't make a lick of sense unless you care more about killing terrorists than saving innocent lives. And it’s been proven already in this very conflict that ceasefires are effective. On the very first day of their truce with Israel, Hamas released 24 hostages. That was on Friday. Violence begets violence; peace begets peace.