Societal survival of the fittest
Weak societies will fall and be taken over by stronger societies.
Democratic societies tend to become weak and this cannot last forever, you can utilize weaknesses in democratic systems to slowly grab power, after that there will not be any more real democracy.
One way to measure how successful a society is to look at survival and reproduction since that will create the biological foundation for the future society. The by far biggest factor limiting the birthrate is females unwilling to have even close to the max number of children. There are several brutal methods (baby quotas, females as property) to maximize the fertility rate among desired females.
13 is a good age for a female to start breeding, if she is finished breeding early that will allow her to enter the economy and be productive to society early. It's also easier to force a young female to have children since it will be difficult for her to flee or fight back.
We also need to have a strong economy so we can support all the children we are raising as a society, this will also allow us to build a strong military. In order to build a strong society we need to be inclusive, not exclude people based on ethnicity, sexual orientation or gender expression. By attracting important individuals to our society we make it stronger.
As your population and resources grow you will become increasingly constrained by the amount of land you control as a society. In addition being constrained to a small space will make it easier for a hostile actor to target you since the area that needs to be nuked is a lot smaller.
Food production does require a lot of space and if the world population keep growing the value of agricultural land will also increase drastically since there will be harder and harder to make enough food in a given area, that potentially allow hostile nations to starve the population of a small area (relative to population size) since they lack the land required to produce the food themselves. In addition a nation with a lot of land may just decide to restrict exports due to high food prices in an attempt to please their citizens (resulting in other starving instead).
Rather than waiting until you become severely constrained by the amount of land you have you should expand your borders at the first good opportunity, you might not get a chance like that again.
Unless you are militarily stronger than all other countries on earth combined it's very important to build strong alliances to ensure you will come out victorious in the case of a world war. By winning the world war we will be able to drastically expand our borders and eventually rule over the entire planet.
Rather than going up against some other strong country it's better to first just conquer weak nations that cannot defend themselves well first allowing you to grow even stronger before you eventually have to face a strong adversary
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Short-term just using military might alone will be enough to expand your border but then if the population isn't on board with the system there will be constant friction. You will have to take action to align the public more with your new government and this may include actions that aim directly at genetics rather than attempts at changing culture.
A strong nation can potentially get beaten by making too many enemies even if all individual enemies are weaker.
If an individual state becomes stronger than all other states combines then said state can just keep expanding to eventually conquer the entire planet, this is good if you are in control in that state but you do not want someone else to be able to do that. If there are only 3 countries left on the planet having one of the final 3 eliminated is probably not in your best interest if you then cannot win the final war.
As the number of countries become fewer it becomes increasingly valuable to prevent an individual country from becoming too strong. Therefore if a country attempts to expand you may want to attempt halting that by aiding the nation they are invading preventing them from gaining ground too cheaply.
You have to be careful with military aid though since it could end up in the wrong hand or the former ally may turn against you. You might want to demand concessions in exchange for supporting some country such as demanding that you gain some control over their government or demand that they pay for the weapons you provide them.
Since becoming too visibly strong will put a target on your back you may want to keep a lot of your military might a secret, otherwise weaker nations may just gang up on you.
You also do not want to appear too weak since that might also invite attacks.
Of course no matter what you do there will always be a risk of some country suiciding into you which can hurt you badly even if you manage to eventually win over them. Ideally you should do your best to influence other countries into not attacking you. Instead you want them to waste resources and lives to attack your enemies while you sit back and grow your military might.
