The Molotov-Ribbentrop Pact .
Poland, on 1 September 1939
germanys invasion of Poland was the last straw in many violations of the treaty of varsailles [ a treaty that severly limited germanys power, established after WWI] and England, fearing an invasion [ especilly since churchill had a large part in aforementioned treaty] so they declared war along with France.
During the 1930's, Britain and France had a defence agreement with Poland. On 1 September 1939, German troops invaded Poland, so on 3 September 1939, in response to that invasion, Britain and France declared war on Germany.
It attacked Poland from the east as part of the nazi-soviet pact.
Well, they kind of declared war on Germany alongside the French, if you want to call that a reaction.
The German invasion of Poland... complements of THE DENNIS JONESGermany invading Polandthe German invasion of Poland
Germanys attack on Poland in 1939
Poland
Mongol invasion of Poland happened in 1240.
The Invasion of Poland was from 1 September - 6 October 1939
I believe it's Blitzkrieg.
There were no reasons for Great Britain declaring war upon Germany other than Germanys invasion of Poland and their refusal to get out when requested to do so. The Polish had a treaty with the British to come to one anothers aid in case of invasion.