Step-by-step explanation:
The invasion of a militarily strong nation over a weaker nation is quite common in history. Same is the case in world war II when Germany invades Poland in 1939.
Failure of league of nations and treaty of Versailles cause discontent among the country, the great depression of 1928 added fuel to the fire.
Germany wanted revenge with the allies of the first world war which was humiliating loss for them. Revenge is again common emotion for wars to begin.
Back in the era there was race of supremacy between Germany and Great Britain. This also lead to the war.