Germany's defeat in World War II was not inevitable, but it depended heavily upon what happened in the Soviet Union. Hitler came very close to overwhelming the Soviets. There were many rumors that Stalin wanted to make a deal with him and let him keep a large tract of land, perhaps the entire Ukraine, as a settlement. Hitler wanted to expand Germany deep into the east and double or treble the size of his country while allowing for a great increase in German population in the future. If Hitler could have defeated the Soviet Union, he would have controlled the entire land mass of Europe and part of Asia. He would have controlled as much of the world as he could use for German expansion in his lifetime. The British could never have hoped to invade Europe, and the U.S. would probably not have gotten involved in the European theater. Hitler was not particularly concerned about defeating the British. He would have been free to carry out his plans to build a Thousand-Reich on the continent and let the British continue to rule their empire, if they could do it. He could have taken his own time about building a huge German navy of super-ships that would make the British navy seem obsolete. The U.S. would almost certainly have gotten into a war with Japan sooner or later, and it would have been easier for the Americans to defeat the Japanese if they were not also involved in fighting Hitler. History could have been entirely different. Germany could have become one of the great superpowers instead of the Soviet Union. It seems as though the British Empire would have had to go into a slow decline, along with France. The British might have been forced to make a settlement with Germany. The U.S. would have probably followed suit. There was no way America could fight Germany on the European continent without a base in Europe, and there would not have been sufficient incentive.
When Hitler invaded the Soviet Union he had fantastic initial successes, capturing millions of Soviet soldiers, driving almost to Moscow and Leningrad. Many Americans thought that war would be over in six weeks. But Stalin was better prepared than the Germans or anybody else realized. And the sheer size of the country, along with the terrible winter weather, helped defeat Hitler in the same way it had helped to defeat Napoleon Bonaparte in the early part of the nineteenth century (an epic struggle Leo Tolstoy recorded in his great novel War and Peace). The Battle of Stalingrad (see reference link below) was the turning point in World War II. It ended in a complete Soviet victory in the winter of 1943, and after that there was no possibility that Germany could have won World War II.
Yes, in my opinion, Germany's defeat in World War II was inevitable because of the Allied strategies. The Allied were closely making plans to help weaken Germany. Such as D-Day and fighting hard on both fronts so Germany would have to split their resources in half. There was no way Germany was able to hold on forever, when America, Great Britain, and Russia pushing Germany back in, and restricting Germany from making much progress.