50 Years

The easiest way to win a game is to start on Very Easy and choose the Greeks. The Greeks have the Minotaur available for purchase from the start. You won't be able to afford him right away, but once you do, he destroys enemies through the majority of the game.

The general mechanics of the game are that your peasants mine gold for you (i.e. give you more money) every time you advance the year. The more peasants you have, the more gold you get per year. Swordsmen and everyone else you can hire are fighters that will be the ones in battle each time. Since you only have a set amount of money, you will need to balance it between getting more peasants (so you can generate more money) and more fighters (so you're sure you'll survive each fight). Don't worry, it isn't nearly as stressful as other simulation/management games.

As you progress through the game, you will periodically be taken to a screen with five columns of perks. While completing the game on this playthrough, choose any column and upgrade it every time (don't spread your upgrades out). You want to upgrade the same perk at least three times for achievements. It doesn't matter which you choose on this playthrough.

Here is the general progression for how to easily beat the game:
 

1. Start by hiring a single swordsman. He'll be able to protect you for some time. Spend the rest of your money on peasants the first year and every year after as soon as you have enough money for more.
2. Every time a fight is triggered, always choose the option 'Fight.'
3. Once you hit a point where the game tells you that you need more food for more peasants, build the required building (as soon as you have enough money) and continue hiring more peasants each year.
4. At Year 8, hire a second swordsman.
5. Around Year 8, you will get a prompt that says "Your scouts have discovered the Chicken Devil altar!" This will happen on every playthrough no matter what. Choose the "Scouting" option. Click on the red guy at the top of the screen to get a popup menu. Choose the option "Deal - killing." This will give you a bad ending at the end of the game but won't impact any achievements, and will automatically kill one enemy per fight before the fight starts, making the game much easier.
6. Around Year 10 you will discover a den. If you haven't unlocked What's in a dungeon? (100G) yet, choose "Scouting" to clear it out. You will very likely lose one of your swordsmen in the process (which isn't a huge deal, since you can still easily finish the game), so if you don't need this achievement, skip this and any other dens you discover to conserve fighters.
7. If you lose a swordsman in the den, immediately hire another one when done so you have two, and then hire a third and fourth by year 15.
8. By Year 15 you should have 4 Swordsmen and 10 Peasants. Start saving up for your Minotaur.
9. By Year 20 you should be able to hire your first Minotaur.
10. Continue to buy the necessary buildings to keep amassing Peasants and Swordsmen.
11. By Year 25 you should have 20 Peasants and 8 Swordsmen (plus your Minotaur)
12. Year 25 or so, build a stable so you can start hiring Knights (stronger than Swordsmen). Prioritize getting 3 of them. You should no longer increase the number of Swordsmen you can hire (but if any die, you can rehire them).
13. By Year 30 you should have 30 Peasants and 6 Knights.
14. By Year 35 you should have 9 Knights and 2 Minotaurs (plus 8 Swordsmen and 30 Peasants from before)
15. By Year 40 you should be up to 15 Knights (plus 2 Minotaurs, 8 Swordsmen, and 30 Peasants). If you have extra money, save it, because you will suffer heavy losses in Year 40. Makre sure you rehire Knights to fill back in whatever you lost.
16. Hire a third Minotaur shortly after Year 40, as soon as you have enough money. Then go up to 18 Knights.
17. Save up money for Year 47, which is a big fight. Recoup your losses from it by hiring back any Knights you lost (and of course and Swordsmen or Minotaurs).
18. Save up money for Year 49, which is another big fight. Recoup your losses from it by hiring back any Knights, Minotaurs, and Swordsmen you lost.
19. This is the end, so use any money you have on more Knights or Swordsmen, whichever you can afford.
20. At the start of the fight on Year 50, choose to "Call on Militiaman" over and over. This summons your Peasants to also fight for you. Do this until all your Peasants are summoned, then start the fight. You should have no problem winning with 3 Minotaurs and 18 Knights (on top of your Swordsmen and Peasants).

That will complete the game and unlock this achievement, along with all story achievements along the way.

The easiest way to win a game is to start on Very Easy and choose the Greeks. The Greeks have the Minotaur available for purchase from the start. You won't be able to afford him right away, but once you do, he destroys enemies through the majority of the game.

The general mechanics of the game are that your peasants mine gold for you (i.e. give you more money) every time you advance the year. The more peasants you have, the more gold you get per year. Swordsmen and everyone else you can hire are fighters that will be the ones in battle each time. Since you only have a set amount of money, you will need to balance it between getting more peasants (so you can generate more money) and more fighters (so you're sure you'll survive each fight). Don't worry, it isn't nearly as stressful as other simulation/management games.

As you progress through the game, you will periodically be taken to a screen with five columns of perks. While completing the game on this playthrough, choose any column and upgrade it every time (don't spread your upgrades out). You want to upgrade the same perk at least four times for achievements. It doesn't matter which you choose on this playthrough.

Here is the general progression for how to easily beat the game:
 

1. Start by hiring a single swordsman. He'll be able to protect you for some time. Spend the rest of your money on peasants the first year and every year after as soon as you have enough money for more.
2. Every time a fight is triggered, always choose the option 'Fight.'
3. Once you hit a point where the game tells you that you need more food for more peasants, build the required building (as soon as you have enough money) and continue hiring more peasants each year.
4. At Year 8, hire a second swordsman.
5. Around Year 8, you will get a prompt that says "Your scouts have discovered the Chicken Devil altar!" This will happen on every playthrough no matter what. Choose the "Scouting" option. Click on the red guy at the top of the screen to get a popup menu. Choose the option "Deal - killing." This will give you a bad ending at the end of the game but won't impact any achievements, and will automatically kill one enemy per fight before the fight starts, making the game much easier.
6. Around Year 10 you will discover a den. If you haven't unlocked What's in a dungeon? (100G) yet, choose "Scouting" to clear it out. You will very likely lose one of your swordsmen in the process (which isn't a huge deal, since you can still easily finish the game), so if you don't need this achievement, skip this and any other dens you discover to conserve fighters.
7. If you lose a swordsman in the den, immediately hire another one when done so you have two, and then hire a third and fourth by year 15.
8. By Year 15 you should have 4 Swordsmen and 10 Peasants. Start saving up for your Minotaur.
9. By Year 20 you should be able to hire your first Minotaur.
10. Continue to buy the necessary buildings to keep amassing Peasants and Swordsmen.
11. By Year 25 you should have 20 Peasants and 8 Swordsmen (plus your Minotaur)
12. Year 25 or so, build a stable so you can start hiring Knights (stronger than Swordsmen). Prioritize getting 3 of them. You should no longer increase the number of Swordsmen you can hire (but if any die, you can rehire them).
13. By Year 30 you should have 30 Peasants and 6 Knights.
14. By Year 35 you should have 9 Knights and 2 Minotaurs (plus 8 Swordsmen and 30 Peasants from before)
15. By Year 40 you should be up to 15 Knights (plus 2 Minotaurs, 8 Swordsmen, and 30 Peasants). If you have extra money, save it, because you will suffer heavy losses in Year 40. Makre sure you rehire Knights to fill back in whatever you lost.
16. Hire a third Minotaur shortly after Year 40, as soon as you have enough money. Then go up to 18 Knights.
17. Save up money for Year 47, which is a big fight. Recoup your losses from it by hiring back any Knights you lost (and of course and Swordsmen or Minotaurs).
18. Save up money for Year 49, which is another big fight. Recoup your losses from it by hiring back any Knights, Minotaurs, and Swordsmen you lost.
19. This is the end, so use any money you have on more Knights or Swordsmen, whichever you can afford.
20. At the start of the fight on Year 50, choose to "Call on Militiaman" over and over. This summons your Peasants to also fight for you. Do this until all your Peasants are summoned, then start the fight. You should have no problem winning with 3 Minotaurs and 18 Knights (on top of your Swordsmen and Peasants).

That will complete the game and unlock this achievement, along with all story achievements along the way.