What was the “secret protocol” of the German-Soviet Non-Aggression Pact?

The secret protocol was a provision of the 1939 treaty between Nazi Germany and the Soviet Union, in which the two countries agreed not to declare war on one another for ten years. The protocol spelled out how Eastern Europe would be divided after Adolph Hitler’s Germany invaded Poland: Germany would control Western Poland, while the Soviet Union would control Eastern Poland the nations of Estonia, Latvia and Lithuania. Less than a week after the pact was signed, Germany invaded Poland. England and France – but not the Soviet Union – quickly declared war on Germany, marking the start of World War II in Europe. Within two years, the Soviet Union joined the fight against Germany, when Hitler violated the non-aggression pact by invading the Soviet Union.

The German-Soviet Nonaggression pact was an agreement signed by Germany and Soviet Union on August 23, 1939 agreeing not to attack each other or support any country that attacked any of them. The pact was proposed by Nazi Germany leader, Adolf Hitler who wanted to invade Poland unopposed. The secret protocol in the pact was the division of Poland territory between the two countries with Germans taking the western part of Poland and Soviets taking the eastern part of the country. Further, the Soviet Union were also given three Baltic states; Latvia, Lithuania, and Estonia as part of the deal.
After the agreement, Nazi Germany invaded Poland without any Soviet Union intervention to the surprise of other European powers. Britain and France declared war on Germany in defense of Poland which eventually lead to the outbreak of the World War II. As the war raged, Adolf Hitler quest to dominate Europe saw the German-Soviet Nonaggression pact violated and the subsequent Nazi Germany invasion of Russia. Later, the Soviet Red Army drove the Nazi forces from their territories.
Further Reading
https://www.history.com/topics/world-war-ii/german-soviet-nonaggression-pact

German-Soviet Nonaggression Pact was an agreement between Germany and Soviet Union where they agreed not to attack each other or support any nation that attacks any of them. The Pact was proposed by Adolf Hitler, Germany leader who wanted to invade Poland unopposed. The secret protocol in the pact outlined the division of the Europe between the two countries. Under the secret deal, German would occupy the western part of Poland through an invasion while Eastern part of Poland would go to Soviet Union. Part of the secret protocol gave three Baltic states; Latvia, Estonia, and Lithuania to the Soviet Union.

according to the agreement, Nazi Germany would invade Poland and Soviet Union would not intervene to help Poland. Due to the aggression of the Germans, Britain and France declared war against Germany to defend Poland that sparked the World War II. During the War, Adolf Hitler violated the pact by invading Soviet Union but was later driven back by Soviet Union forces.


References
https://www.history.com/topics/world-war-ii/german-soviet-nonaggression-pact

The German-Soviet Nonaggression Pact was an agreement between Nazi Germany and the Soviet Union. In the pact, both sides agreed that they would not go to war with each other, nor would they support any nation that attacked either of them. The secret protocol of the German-Soviet Nonaggression Pact dealt with the division of Europe between the two nations. As a result of the agreement, Germany would receive the western part of Poland, following Hitler's invasion, and the Soviet Union would gain the eastern part of Poland. The Soviet Union would also gain the Baltic states of Lithuania, Estonia, and Latvia.
Shortly following the agreement, Germany invade Poland with the knowledge that the Soviet Union would not intervene. This caused Britain and France, who had proclaimed they would defend Poland, to declare war against Germany. This sparked World War II. After only approximately two years, Hitler would violate the German-Soviet Nonaggression Pact and invade the Soviet Union.
https://www.history.com/topics/world-war-ii/german-soviet-nonaggression-pact