Interesting.
I presume "breakthroughs" mean revolutionary designs, which have a major impact on golf course architecture? Or does it mean a "new" course designer "breaking onto the scene" with a particular course?
OFF THE TOP OF MY HEAD, here are my thoughts on "breakthroughs"... meaning revolutionary designs, which have a major impact on golf course architecture, per decade:
1900-09 = Sunningdale; Willie Park Jnr.
1910-19 = National Golf Links of America; C.B. Macdonald
1920-29 = Royal Melbourne; Alister Mackenzie
1930-39 = Augusta National; Alister Mackenzie/Bobby Jones
1940-49 = Peachtree; Robert Trent Jones/Bobby Jones
1950-59 = Oakland Hills-South (redesign); Robert Trent Jones
1960-69 = Harbour Town; Pete Dye
1970-79 =
![Huh? ???](http://golfclubatlas.com/forum/Smileys/classic/huh.gif)
1980-89 = TPC Sawgrass; Pete Dye
1990-99 = Sand Hills; Bill Coore/Ben Crenshaw
Again, this was completely OFF THE TOP OF MY HEAD... it's amazing that similar names pop up. Mackenzie. Jones. Trent Jones. Dye. Very interesting.