where are all the men able to fight these wars coming from? Didn't Westeros take a massive hit with the War of the 5 Kings? Like i'd imagine the 15-45 male demo is drastically reduced.
For the main two kingdoms constantly featured at war, the Lannisters and the Starks, yeah, they really should be down to practically no ability to prosecute a war. With The North, they at least went out of its way to establish that the armies at the Battle of the Bastards were several sizes smaller than the forces commanded by Robb before the Red Wedding, by keeping Jon's force tiny and limiting Ramsey to only three houses. Plus the North is now being portrayed as turtling up for the Winter, training everyone they can and focusing on insular security.
It's the Lannisters who should effectively be toothless by now; their forces are supposed to only barely outsize the Stark's when both are fully mobilized, and while they didn't suffer the Red Wedding, they did lose several battles to Robb while scrambling to hold the Red Keep against Stannis, and right now they're supposed to be occupying at least three kingdoms (their home in the Westerlands, the Frey-less Riverlands, and the region around Kingslanding), and maybe even a fourth (we've got no information for what the Stormlands are like right now).
The show putting such emphasis on Jaime recruiting the Tarlys is supposed to answer the incredible disparity they'd experience against the Tyrells; yes, the Tyrells have been decapitated as a great House, but the Reach is still one of the most untouched Kingdoms and frickin'
huge. Even if the Tarlys turn on Olenna, there should still be so many other major Houses with troops left to support that a civil war would be more likely than a swift change in power. And it still boggles the mind that the highly PR conscious Tyrells command so little loyalty from Reach lords after being flat out murdered by an outsider blowing up a church, while over in Dorne, a bunch of base-born kinslayers can apparently command a whole country.
Seriously, so much Dornish drama could have been avoided by just leaving Doran Martel as his country's leader.