A self-proclaimed "left dissident Marxist", Mayer's major interests are in modernization theory and what he calls "The Thirty Years' Crisis" between 1914 and 1945. In Mayer's view, Europe was characterized in the 19th century by rapid modernization in the economic field by industrialization and retardation in the political field. Mayer has argued that he calls the "Thirty Years' Crisis" was caused by the problems of a dynamic new society produced by industrialization facing a rigid political order. In particular, Mayer feels that the aristocracy in all of the European countries held far too much power, and it was their efforts to keep power that led to World War I, the rise of fascism, World War II, and the Holocaust.
In a 1967 essay "The Primacy of Domestic Politics", Mayer made a
Primat der Innenpolitik ("primacy of domestic politics") argument for the origins of World War I. Mayer rejected the traditional
Primat der Außenpolitik ("primacy of foreign politics") argument of traditional diplomatic history under the grounds that it failed to take into account that in Mayer's opinion, all of the major European countries were in a "revolutionary situation" in 1914, and thus ignores what Mayer considers to the crucial impact that domestic politics had on foreign-policy making elites. In Mayer's opinion, in 1914, the United Kingdom of Great Britain and Ireland was on the verge of civil war and massive industrial unrest, Italy had been rocked by the Red Week of June 1914, the French Left and Right were waging a war to the death with each other, Germany was faced with ever-increasing political strife, Russia was facing a huge strike wave, and Austria-Hungary was confronted with rising ethnic and class tensions. Moreover, Mayer insists that liberalism and centrist ideologies in general were disintegrating in face of the challenge from the extreme right in the UK, France and Italy while being a non-existent force in Germany, Austria-Hungary and Russia. Mayer ended his essay by arguing that World War I should be best understood as a pre-emptive "counterrevolutionary" strike by ruling elites in Europe to preserve their power by distracting public attention onto foreign affairs.
In his 1967 book
Politics and Diplomacy of Peacemaking: Containment and Counter-Revolution at Versailles, Mayer argued that the Paris Peace Conference was a struggle between what he calls the "Old Diplomacy" of the alliance system, secret treaties and brutal power politics and the "New Diplomacy" as represented by Vladmir Lenin's Peace Degrees of 1917 and Woodrow Wilson's Fourteen Points, which Mayer sees as promoting peaceful and rational diplomacy. Mayer argued that in 1919, the world was divided between the "forces of movement" behind the "New Diplomacy", representing liberal and left-wing forces and the "forces of order", representing conservative and reactionary forces behind the "Old Diplomacy" Mayer sees all foreign policy as basically a projection of domestic politics, and much of his writing on international relations is devoted towards explaining just what domestic lobby was exerting the most influnce on foreign policy at that particular moment of time" In Mayer's view, the "New Diplomacy" associated with Lenin and Wilson (whose 14 Points Mayer sees as a hasty liberal attempt to respond to Lenin's Peace Degrees) was associated with Russia and America, both societies that Mayer has argued either had destroyed or lacked the partial "modernized" societies that characterized the rest of Europe Mayer sees US diplomacy at Versailles as an attempt to posit a "new", but "counter-revolutionary" style of diplomacy against "revolutionary" Soviet diplomacy In Mayer's view, the greatest failure of the Versailles Treaty was that it was a triumph for the "Old Diplomacy" with a thin "New Diplomacy" veneer. The principal reason for this according to Mayer was he considered to be the irrational fears generated by the Russian Revolution, thus leading to an international system designed to contain the Soviet Union. A major influence on Mayer is the late British historian E. H. Carr. In 1961, Mayer played a key role in having an American edition of his friend and mentor's book,
What is History? published. Many of Mayer's writings on international affairs in the interwar era take as their starting point Carr's 1939 book
The Twenty Year's Crisis.
In his 1981 book,
The Persistence of the Old Regime, Mayer argued that there was a "umbilical cord" linking all the events of European history from 1914 to 1945. In Mayer's opinion, World War I was proof that: "The forces of the old order were sufficiently willful and powerful to resist and slow down the course of history, if necessary by recourse to violence". Mayer argued that because of its ownership of the majority of the land in Europe and because the middle class were divided and politically undeveloped, the nobility continued as the dominant class in Europe. Mayer argued that faced with the challenge of a world in which they had lost their function, the aristocracy both embraced and promoted reactionary beliefs such as Nietzsche and Social Darwinism together with a belief in dictatorship and fascist dictatorship in particular. In Mayer's view, "It would take two world wars and the Holocaust...finally to dislodge the feudal and aristocratic presumption from Europe's civil and political societies".
In his 1988 book
Why Did the Heavens Not Darken? Mayer argues that Adolf Hitler ordered the Final Solution in December 1941 in response to the realisation that the Wehrmacht could not take Moscow, hence ensuring Nazi Germany's defeat at the hands of the Soviet Union. In Mayer's opinion, the "Judeocide", as Mayer calls the Holocaust was the horrific climax of the “Thirty Years' Crisis” that had been raging in Europe since 1914.
The Holocaust, which Mayer refers to as the "Judeocide", is viewed by him primarily an expression of anti-communism. In his book, Mayer wrote:
"Anti-Semitism did not play a decisive or even significant role in the growth of the Nazi movement and electorate. The appeals of Nazism were many and complex. People rallied to a syncretic creed of ultra-nationalism, Social Darwinism, anti-Marxism, anti-bolshevism, and anti-Semitism, as well as to a party programs calling for the revision of Versailles, the repeal of reparations, the curb of industrial capitalism, and the establishment of a völkisch welfare state"
Mayer's purpose in writing
Why Did the Heavens Not Darken? was in his words to put an end to "cult of remembrance", which in his view had "become overly sectarian" with too much focus on Jewish suffering and on the Jewish dead Mayer has often accused Israel of exploiting the memory of the Holocaust to further its foreign policy objectives In Mayer's opinion, Hitler's war first and foremost against the Soviets, not the Jews. According to Mayer, the original German plan was after the German victory over the Soviet Union to deport all the Soviet Jews to a reservation behind the Urals
In regards to the functionalist-intentionalist divide that pervades Holocaust historiography, Mayer's work can be seen as a bridge between the two schools. Mayer argues that there was no masterplan for genocide, and that the Holocaust cannot be explained solely in regards to Hitler's world-view. At the same time, Mayer agrees with those intentionalist historians such as Andreas Hillgruber (with whom Mayer otherwise has little in common with) in seeing Operation Barbarossa, and the Nazi crusade to annihilate "Judeo-Bolshevism" as the key development in the genesis of the "Final Solution to the Jewish Question".