What directly led to Hitler's invasion of Poland?

In my point of view both the Munich Agreement and the invasion lead to the beginning of World War 2. But the main cause of the war was the invasion of Czechoslovakia in 1939. Both of these incidents clearly show that both UK and France and the German leader Hitler could not be trusted anymore. Furthermore, it is clearly seen that the invasion of Czechoslovakia was the main event leading to the war because it made Hitler …

…only thinking to take back what they have lost after the World War One, but to take over the world, which also contributed to the out-break of the World War Two. In conclusion, the Munich Agreement and the invasion of Czech had both caused the war, but the invasion eventually convinced Hitler to fight other nations to Poland, which provoked Britain and other countries to declare war on Germany and finally started World War Two.