Hamas is the aggressor in the most recent war. They invaded Israel on Oct 7 2023 and killed 1200 people. If you adjust this for population that would be like Mexico invading the US and killing 41,000 people.
Israel has killed more than 50,000 Palestinians in Gaza.
If you adjust for population, that's like Mexico bombing nearly every building in the US and killing 8 million people.
Hamas is the aggressor only in a very immediate sense. Israel holds millions of Palestinians under military occupation, steals more and more of their land over time, and kills Palestinians all the time. From January 1st through October 7th 2023, when there was no war going on, Israel killed 234 Palestinians in the West Bank. That's just business as usual for Israel.
