It absolutely was not inevitable even though it has often been presented as such. To which degree differs. I've seen a lot of history books, often intended for use in schools, that simply present it as an inevitable result of WWI without ever elaborating on why but it really doesn't stop there. There are actually real historical models that to varying degrees consider WWI and WWII to be parts of the same war. Primarily they are;

The Long War-theory (as proposed by Philipp Bobbitt in The Shield of Achilles: War, Peace, and the Course of History) which considers virtually the entire 20th century as a single continuous conflict starting with WWI and ending with the decline of the Soviet Union.

The Second Thirty Year's War-theory (Sigmund Neumann in The Future in Perspective, but also popularized by among others Charles deGaulle and Winston Churchill) which presents WWI and WWII as a single war with the intermittent years explained through colonial and regional conflicts that tie into WWII.

The European Civil War-theory (which was formalized by Paul Preston in The Republic Besieged: Civil War in Spain 1936–1939 but has been talked about and mentioned long before Preston's work) which sees virtually all the European conflicts between the Franco-Prussian war and the end of WWII as a single tumultuous civil war in Europe.

While all these theories do have their merits they do not represent the mainstream view among historians today. They might help you understand how conflicts tie into each other from a certain perspective but in my opinion they all rely on gros over-simplifications or intentionally ignore all manner of facts that don't support their case.

Aaaaanyway, back to the main question here. Was WWII the inevitable result of WWI? The oft-presented case is that the terms set by the victors of WWI were so harsh that another war was essentially unavoidable. However, this theory completely disregards the fact that everyone in the interwar years were well aware of this and renegotiations of the reparations and restrictions imposed on Germany in the Treaty of Versailles were well under way by the mid 1930's. I won't go super far into the details here but between the Young-plan and the Dawes-plan the reparations owed by Germany had been reduced from 132 billion gold marks to 713 million (or by 99,5% to put it in perspective).

Added to this there were also substantial loans granted to Germany, primarily by Wall Street to help with reconstruction. When Hitler passed what amounted to the "Liberty Law" proposed by the conservative block in the Weimar Republic (essentially renouncing all war guilt and defaulting on future reparations and loans) the US had actually paid more money to Germany than Germany had paid to the victors.

So was war inevitable? Abso-fucking-lutely not. The war was intentionally brought on by the policies and decisions of Hitler and the Nazi party and to my mind, any attempt at presenting it as "inevitable" is often tied to right wing revisionism.