A staged attack on a radio station
On the night of 31 August 1939, German operatives staged an attack on a radio station near the border town of Gleiwitz, dressing personnel in Polish uniforms to fabricate evidence of Polish aggression that Germany then used as its public justification for invading the following morning. The invasion itself lasted thirty-five days, from 1 September to 6 October, and relied on newly developed blitzkrieg tactics, coordinated tank divisions supported by dive bombers, that punched through Polish lines and encircled isolated units rather than advancing along a single continuous front, a method that let roughly twenty-seven hundred German tanks and over two thousand aircraft overwhelm Polish defences considerably faster than traditional infantry warfare would have allowed.
A secret protocol made public later
What made the invasion possible diplomatically was a secret protocol attached to the Molotov-Ribbentrop non-aggression pact, signed in Moscow on 23 and 24 August 1939, which divided Eastern Europe into German and Soviet spheres of influence and specifically apportioned Poland along a line running through the Pisa, Narew, Vistula, and San rivers. That protocol remained hidden from the wider world for years, its existence and precise terms only becoming public when they surfaced during the Nuremberg trials after Germany’s 1945 defeat, meaning contemporaries in 1939 could see the invasion’s military coordination but not the full extent of the prior diplomatic arrangement that had made it possible.
Tanks and aircraft outpacing defence
The Soviet Union invaded from the east on 17 September, two and a half weeks after Germany’s initial attack, acting on the pact’s secret territorial division rather than in direct coordination with German battlefield movements, and Polish forces, already overwhelmed on their western front, had little capacity left to resist a second invasion from the opposite direction. German losses in the campaign totalled roughly sixteen thousand killed against Polish losses near sixty-six thousand killed and close to seven hundred thousand captured, while Soviet forces entering from the east suffered comparatively minimal casualties, a lopsided distribution that reflects how thoroughly Poland’s defences had already been broken before the second invasion even began.
Genocide named in the orders themselves
The invasion’s significance extends beyond its military outcome because of explicit instructions historians attribute directly to Hitler, ordering forces to kill without pity or mercy all men, women, and children of Polish descent or language, language cited as establishing genocidal intent from the campaign’s outset rather than something that emerged only later during the occupation period. That framing matters for how historians categorise the invasion: not simply a conventional territorial conquest but one whose foundational orders already anticipated mass civilian killing as a deliberate policy tool rather than an unfortunate byproduct of conventional warfare.
Two invasions, one week apart
The pact’s secret protocol was, by the account of British diplomat Alexander Cadogan’s own contemporaneous diary, received in London as a genuine shock, recorded simply as a black day, a reaction that reflects how completely the German-Soviet alignment upended prior Western assumptions about the two powers’ mutual hostility. Historian Geoffrey Roberts has called the pact one of the most stunning reversals in diplomatic history, a characterisation that captures how thoroughly it removed, at least temporarily, the possibility of the two-front war Germany would otherwise have had to plan around, freeing it to concentrate its full military weight against Poland and then, the following year, against Western Europe.
A shock recorded in real time
The invasion is worth studying closely both for what it reveals about how a war’s pretext can be manufactured and documented well enough for later historians to dismantle entirely, and for how directly its own founding orders anticipated the atrocities that followed rather than leaving them to develop separately. Reading the invasion alongside the pact that enabled it, and alongside the later collapse of that same pact when Germany invaded its supposed Soviet partner in 1941, gives a fuller sense of how contingent and calculated the entire opening phase of the European war actually was, rather than the more familiar version that begins simply with tanks crossing a border.