Inspired by a comment by @Evargalo on this question, I ponder how long a sequence can last where each turn, White has more available moves than the previous turn, in a situation with only White pieces present on the board. With no Black pieces to add moves via potential captures with, it is interesting to wonder how the geometry of the pieces' powers can be manipulated.
Here is a short 37 moves to demonstrate the possibilities.
[FEN "8/8/8/8/8/8/PPPPPPPP/RNBQKBNR w KQ - 0 1"] 1. b3 Nc7 2. c4 Ne8 3. a4 Nc7 4. h4 Ne8 5. g3 Nc7 6. Rh2 Ne8 7. f4 Nc7 8. d3 Ne8 9. Qc2 Nc7 10. e3 Ne6 11. e4 Nc7 12. f5 Ne8 13. d4 Ng7 14. e5 Ne8 15. f6 Nc7 16. h5 Ne8 17. h6 Nc7 18. h7 Ne8 19. h8=Q Nc7 20. f7 Ne8 21. e6 Nc7 22. d5 Ne8 23. a5 Nc7 24. a6 Ne8 25. a7 Nc7 26. e7 Ne8 27. c5 Nf6 28. c6 Ne8 29. c7 Nf6 30. a8=Q Ne8 31. d6 Nf6 32. d7 Ne8 33. b4 Nf6 34. c8=Q Nd5 35. d8=Q Nf6 36. e8=Q Nd5 37. f8=Q
(In order to animate this "properly", I cheated a little bit. I used apronus.com to play Black without a king, and then edited out the Black knight when creating this question, and the replayed still plays White's moves without question, thus nullifying the need to type/paste "null" for each Black move).