Five (!) vertical fifteens shred the grid, leaving, in one reviewer's opinion, somewhat strange-looking black blocks that also run vertically. Maybe there should be more vertical themes, but they are like vertical photographs, I guess, which is to say, less common than horizontal ones.
MANIFESTDESTINY (3D: Expansionist doctrine) went right in, probably because it took me so long to understand that term in History class, which resulted in me really understanding it. I also thought immediately of THRILLAINMANILA (9D: Big 1975 boxing showdown), because I'm old and I have brothers who watched boxing, but I thought of it with the "The," as I always do, so it took a cross or two before I figured that one out. I am not familiar with THEDESCENTOFMAN (11D: Darwin work … with a hint to three consecutive letters in 3-, 4-, 7-, 9- and 11- down), but it wasn't too hard to figure out.
I don't particularly love the clue "14A: Knock silly" for DAZE, nor with "19A: Honest with" for TRUETO, but, well… what am I gonna do? I chuckled momentarily at CAB (38A: One with a checkered existence?) and UMP (52A: Official with a whisk broom, for short) (is it really a broom or a brush?), groaned at AND (43A: First-goal link), and enjoyed the three two-word sentence INONIT (45A: Privy to a practical joke, say). There's some deep Simpsons trivia in MONA (37A: Homer Simpson's mother) (I needed crosses for this!), and deep Native American trivia with 50A: Onetime tribe of the Upper Midwest (SAC) (ditto).
Lots of the usual stuff in here, and some of the not-so-usual-but-it's-really-better-that-way stuff (EZINE, ANTIS, ATRIA…), but, well, I don't know… it's Wednesday, I guess.
p.s. After I write the blog, I often go see what Amy Reynaldo thought of the puzzle, and she points out that the letters "MAN" not only appear in every theme answer, but move progressively (descend) lower and lower, which is a really nice touch. Still, the density of theme material, and the added bonus theme element, really compromise the rest of the fill. Is it worth it? Again, it's Wednesday, so maybe.