To be sSpecifically, your country should ownpossess a super powerful military.

Your original sentence is grammatically correct. Logically however, ‘possess’ would be a better word than ‘own’.

With a strong military, your country won't be invaded by others, and it'which is the foundation of any nation.

When linking together an independent clause to dependent clause, ‘which’ or ’that’ is preferable instead of ‘and’ . ‘And’ typically connects two clauses of equal value.

I like to watch movies and go hiking.
A nation is only as strong as its leader, and a leader is only as strong as his people.

With a lot of money, your country can develop theit’s economy, science and technology, education, and medical care and so onsystem.

I also believe that there are many people who canould be presidents, but the key is how they can get that position. The key difference between you and them is opportunity.

Even cutting off morif we assume thant half the population of one country is incompetent, there are still many people who are capable of being a president, let alone other government officials.

So never admire those who have a higher position than you, they are not necessarily as capable as you, y. You just don'idn’t have thateir opportunity.

In my opinion, being a president is so easy in that all you have to do are just two things.

Even cutting offexcluding more than half the population of one country, there are still many people who are capable of being a president, let alone other government officials.

"Cutting off" does not fit in this sentence.

So neverdo not admire those who have a higher position than you, they are not necessarily asmore capable asthan you, you just doidn't have thate same opportunity.

I rewrote to sound a bit more native.