Depending on where you are in the research tree, your ability to build up your military can vary. Upgrade techs in the tree will allow you to upgrade the various military buildings and by doing so you will increase the number of troops you can train at one time and shorten the length of time it takes to train them. I'm an elf, so not sure of the names of all the buildings/wonders for humans, but there is always a comparable building/wonder. The Wiki has good descriptions of all of them. I'm in fairies, and this is what I've learned so far:
Tournament squad sizes are much smaller than your regular squad sizes for world map exploration, so you have a lot more squads in tournaments even with the same number of actual troops. Building up your military takes upgrading barracks/training grounds/mercenary camp so training times are shorter. There are also Ancient Wonders that decrease training time (Needles of the Tempest, maybe more, but I can't think of them right now, lol!) But, with shorter training times, sometimes your training queue will run out overnight, so you train less troops due to idle time. You can impact this by building/upgrading armories so you train more troops at one time, thus increasing the time, but having more troops at the end of the time. You can also impact the number of troops trained by building Ancient Wonders: Dwarven Bulwark (get at end of Dwarves) increases training size as does Shrine of the Shrewdy Shrooms (get at the end of Orcs). There are other Wonders that influence your military as well. Martial Monastery, for example, improves troop health, so it helps keep troop losses in battle lower as does learning to manually fight as
@dirtydokken mentioned.
There is a very detailed battle guide by Mykan in the sticky threads at the top of this Battle Help forum. It took me awhile to wrap my brain around the information in there (still learning!), but it is well worth the time. Here is a direct link:
https://us.forum.elvenar.com/index.php?threads/mykans-guide-fighting-guide.4205/