Devarim - Chamishi
Land of the Giants
God told the people to travel north. They were to be cautious of Eisav's descendants. Yes, the people of Seir feared the Jews, but they were not to confront them as Seir was Eisav's inheritance, not Israel's. The Jews could purchase food and drink from Seir as they passed through, which they did without incident.
When they came to Moab, God gave them the same instructions. They were not to start up with the Moabites because that land was given to the descendants of Lot. (We are told that the land of Moab had previously been inhabited by a race of giants, although that's neither here nor there.) This was 38 years after the decree of wandering in the desert. (Since that was in the second year in the desert, it places these events in the final year of the exodus.) The older generation had already died out by this time.
They came close to the territory of Ammon. God gave them to same directive (i.e., to come in peace) since that land also belonged to descendants of Lot. (This, too, had previously been a land of giants, but God got rid of them before the Ammonites moved in.)
When the nation came to the land of the Amorite king Sichon, THEN they were told to wage war, as that land was given to the Jews. They sent messengers to Sichon, requesting permission to pass through peacefully as they had done elsewhere. When he refused, it was "go" time.