AI as a field initially started getting big in the 1960s with machine translation and perceptrons (super-basic neural networks), which started promising but hit a wall basically immediately. Around 1974 the US military cut most of their funding to their AI projects because they weren't working out, but by 1980 they started funding AI projects again because people had invented new AI approaches. Around 1984 people coined the term "AI winter" for the time when funding had dried up, which incidentally was right before funding dried up again in the 90s until around the 2010s.