Why did God slay so many in the old testament?

[Gary K]

Indeed their probation was up - but also Israel would be "moving in" so either those two nations were going to convert to worship the one true God - or they were going to corrupt Israel and they themselves would not turn back from rebellion.... or they would be wiped out having already passed the time allotted for their probation (Like Sodom and Gomorrah )

I've been thinking about this thread a fair amount.

The Israelites were known to all of the nations of Caanan. Those peoples were all aware of Noah's curse upon Ham and his grandson Caanan as well as the blessing upon Shem and his descendants by Noah. They knew they were prophesied to be the servants of descendants of Shem. And they knew the Israelites were the descendants of Shem. There had to be a lot of hatred for Israel and rebellion against God under those circumstances within the nations of Caanan.

It's no wonder, to me, that probation for both the Amalekites and Amorites closed because they came out to wipe out the Israelites at their first meeting with Israel. Moses went way out of his way to be agreeable with both nations and their response was we are going to kill all of you.