How could Hitler have avoided war with France and Britain?
When Hitler invaded Poland, the French & the British had already declared war on Germany. However, the beginning of this period was calm, with neither side attacking each other. This standoff unfortunately couldn't have continued since the allies were blockading Germany.
I believe the invasion of France was necessary in order to gain ports & make naval blockades more difficult. I believe, Hitler could have done away with the Battle of Britain if he had focused his energies on sinking British convoys & seizing Iceland in order to starve the island nation. Then, the island nation could be starved into making a peace deal.
After this, he should have focused his energies on improving relations with the US. He could also have avoided war with the USSR or atleast fought a more a successful conflict with the soviets by starving them of resources. This could be achieved with the US remaining neutral or helping the Axis in blockading or sanctioning the USSR. After all, the Red Navy & the Red Air force were inferior to the Axis navies & air forces , it was only the Red Army that could stand up to the Axis forces.
War with France was always a part of the grand plan for Germany. It was thought that if Germany controlled continental Europe Britain would agree to a treaty ceding Germanys right to control its conquered territories while Germany would leave the British Empire alone. Having seen Britain cravenly sell out Czechoslovakia in spite of solemn treaty obligations, Hitler was confident that they would do the same with Poland. In short, nothing Hitler could have done would have averted war witth the UK and war with France was already on the books.
It should be pointed out though that the General Staff planned for a war to begin in 1944-45 after a substantial buildup of its armed forces, especially the Naval arm. Hitler jumped the gun
Not starting a war with France and Britain, essentially.
Hitler knew that the invasion of Poland would trigger a war with the Western allies, since he was well aware of the Anglo-Polish military alliance. This was something he planned on: signing the Molotov-Ribbentrop pact was the acknowledgement that war with France and Britain was going to be an inevitable consequence of German plans for conquest. And like a student of German history, Hitler followed Bismark's dictate to avoid simultaneous war with France and Russia.
That being said, he didn't expect them to fight quite so hard.