Fusion changed from the twinkle in the eye of 1900's scientists with the invention of Quantum Mechanics by the acceptance of light photons as particles, not just of light as waves, by way of Albert Einstein paper in 1905. From photons came atoms. The mysteries of the first known particles, in the 1800's, Beta and Gamma Rays were changed from Rays to particles, as Beta particles were found to be 'fast' electrons from nuclear decay inside the atom's nucleus, and 'some' Gamma Rays are 'fast' Neutrons from the same source. With the discovery of the atom, and it's nucleus, the origin question arose, as it always does with mankind's curiosity.
The big three highlights are briefly listed. In 1932 to 1934, laboratory fusion was first performed by three scientists; Oliphant, Harteck, and Rutherford. In 1948, Alpher–Bethe–Gamow paper argued the Big Bang would create hydrogen, and by fusion would create helium and heavier elements. In 1957, Margaret Burbidge, Geoffrey Burbidge, William A. Fowler, and Fred Hoyle wrote the famous B2FH paper on stellar nucleosynthesis, proposing what few thought was true, fusion powered the Sun, which main stream physicists slowly came to accept as true.
After World War II's explosion of a nuclear and a thermonuclear (combines fission and fusion) bomb, the rush was on to learn everything about fusion. In 1958, these learning efforts were 'partially' declassified by Russia, followed by the United Sates. Why? Fusion alone could not make a more powerful bomb than thermonuclear. The next big push was converting the war time issue of fusion into finding a peace time use, generating electrical power, also called "fusion power." Focus was on creating the same type of fusion as powering the Sun. A star in a bottle was the goal. Was it even possible? The needed temperature, density and confinement time was so very high.
The dream of mankind, to have unlimited power, heat, light, food, clothing and shelter fascinates children, and more so, adults. Out of World War II's effort for the 'bomb', from fission of heavy Elements, came the idea that power of that magnitude was also available from fusion of light Elements. The birth of the thermonuclear bomb, part fusion, part fission, around 1944, lead to fusion's classification by United States and Russia. The United States unclassified most their fusion research in 1958, once the scientist were convinced that fusion alone could not make a 'bomb.' The first fusion textbooks were published. And the world could read about fusion, and many prophets said unlimited power generation from nuclear energy was going to rush in an era of wealth.
Russia recently unclassified a little of their late 20th century fusion research, but an unknown amount remains classified. Behind the Iron Current, during the late 1940's through to the 1990's, Russian fusion research remains an enigma. Many European and Russian scientists, caught behind the Iron Current, pushed forward technology to create fusion in the laboratory. The Tokamak was born, a Russian scientist's idea, and many years later was accidentally leaked to an American scientist, who told the world. Main stream physicists thought the Tokamak's greater efficiency over other fusion power reactor designs would succeed. All other types of fusion reactors were unfunded, by both governments and universities, from the 1990s to 2005.
From 2006 through 2016, has seen a slowly renewed interest in non Tokamak reactor designs to generate power, that is generate electricity. American government funding for new designs started in 2017, and continues through 2024 with around 20 firms receiving USA ARPA-E (2007 to now) and DOE tax dollar funds. In 2010, USA created the DOE department of Fusion Energy Science office (FES), just to fund alternate fusion efforts.
This brief history highlights only a few key milestones that fires the imagination of mankind.