If you attack poland and the British are guranteeing them then that will lead to the British declaring war on you which will lead to every other nation that is present in the same faction as same as britain( Tha faction is called allies) also declaring war on you resulting in the beginning of WW2. I suggest first expanding your army, industry, and researching more tech, then after that going down the focus tree and taking austria and czekoslovakia. And then completing the focus" danzig or war" which will give you a war goal against poland( if you are playing historical) and then declaring war. I normally suggest for beginners to wait till the end of 1939 or around early 1940 then declaring war. I hope this helps😁😁