September 1, 1939 | Hitler invaded Poland; thus began World War II in Europe
At 4:45 a.m., some 1.5 million German troops invade Poland all along its 1,750-mile border with the German-controlled territory. Simultaneously, the German Luftwaffe bombed Polish airfields, and German warships and U-boats attacked Polish naval forces in the Baltic Sea. Nazi leader Adolf Hitler claimed the massive invasion was a defensive action, but Britain and France were not convinced. On September 3, they declared war on Germany, initiating World War II.
There is an untold history between Germans and Poles that goes back a long way. Let us keep it short and say, in the 1800's there were a series of slaughtering taking place by the Germans against the Poles. Then things stabilized a bit until WW1 broke out and Poland was re-formed after the war. The problem now was there were Germans inside Poland that owned large area's of land and were not ever really considered Polish Citizens.
After WW1 small groups of Poles began an anti-German campaign against these Ethnic Germans. In Germany hate campaigns also began to circulate against the Poles. But the bigger threat to Poland was and always had been Russia.
They had a saying in Poland,
"With the Germans, we will lose our freedom, with the Russians we will lose our souls"
Enter Hitler. Hitler and Pilsudski both saw the advantage of working together against a common threat, the problem here was their respective populations were not 100% behind this mutual assistance. So issues were slow to be resolved, but they were moving forward.
After Pilsudski's (1937) death the Polish Government totally reversed it's diplomatic negotiations with Germany and suddenly started opposing all and any proposals. Including the Danzig issue and the use of railways that Germany used to interact with East Prussia. It was also during this time when Polish Nationalists decided to aggressively harass German Ethics again, but this time thief, confiscation, unlawful imprisonment, beatings, vandalism, and murder were on the menu.
Germany documented all of the aggressive actions and protested to the League of Nations, it was ignored. Most the western press refused to investigate and report on the atrocities, but a few did, including and not limited to France, Britain, Belgium, Sweden, and Denmark. Even the Russians acknowledged it. At the same time, the diplomatic negotiations were also attempted and ignored by the same press.
Between 1920-1939 more then 1 million Germans were displaced or given refugee status, most of these were in the former West Prussia area, but other groups like Ukrainians and Czechs were affected as well. This is also when the first European concentration camps were built, by Poland. Events like the Danzig Crisis and Polish aggression combined with Poland's absolute refusal to negotiate in good faith brought things to a head in 1939.
Rydz-Smigly Statement was EDITED OUT due to someone pointing out it could be false, believably.
Just before the invasion German began to get reports of German Ethnics being slaughtered by a few radical Polish Groups with the backing of the Polish Government. This is when Hitler attacked. He mentioned it before, during, and after the takeover. It was well documented but blown off in the propaganda wheel. After the brief war, the physical evidence began to be collected.
The Germans invited the whole world to witness the investigations, few sent representatives. Many more wanted to make sure this evidence was proclaimed to be false and lies. The Bromberg Bloody Sunday event, however, was so big and impossible to cover up it was downplayed instead and few so-called history books even talk about it. Autopsies reviled some of the corpses were in a state of decay they predated the start of hostilities.
Wittiness statements were collected in great detail as well as confessions from those who committed them. I agree with the means to interrogate these prisoners and criminals was probably not on today's standards. Pictures were also collected and some were defiantly determined to be false, so others that could not be 100% confirmed were also not used as evidence. Germany did not intend to falsify any evidence used simply because Hitler still hoped to stop the war, make peace with Britain and concentrate on the Communists with Britain as an ally.
The end result was the Germans estimated somewhere around 58,000 Ethnic Germans were either "missing" or killed. Captured German soldiers were found tortured to death or just killed and mutilated. Again, the German evidence of this was largely ignored and dismissed as propaganda. I do agree the reports are not 100% accurate and the numbers are skewed but not to the extent some will tell you.
Now with all this said there is a question to be asked and answered. What would possibly embolden Poland with it's smaller army to provoke Germany? Simply put, Britain and it's lapdog France. Looking at the grand scheme of things worldwide, Germany and their new-found piety was a direct threat to both the British and French Empires, it was also a direct threat to Centralized Banking, which was abolished in Germany by the National Socialist. The Allies had Poland believing that any action they took would be 100% backed by them and they would, therefore, be under the protection of them should Germany react militarily. Well, they did indeed react, just not in a way that had any intention of actually helping Poland, but that's another discussion.