Today's money supply is taken care of by private institutions such as 'Central Banks' or 'Federal Reserves' but it hasn't always been like that. Indeed, for example, in the US, former presidents such as Jackson or Lincoln had tried to implement 'free-of-debt' money issued by the government (i.e. "green bucks").
As far as I'm aware, Andrew Jackson was a strong proponent of decentralised power (small government) and hard money. Lincoln was a nationalist (big government) that created a fiat money (not backed by gold/silver, can be used to pay taxes (legal tender)) called the "green-back" (because the ink used on the reverse side was green).
Nowadays, it seems that debt had clearly become out of control, making it even impossible to pay its interest.
Citation?
But I dont get it, as everything that has been lent so far, it has to eventually be repaid (+interest). So how and with what can we even repay the interests since we dont create the money to repay them?
Simple. You earn more money to pay the interest. If the bank that lent the currency into existence simply destroys it when it's repaid then it will be impossible to pay the interest. If, instead, that bank spends the repaid currency on hookers and blow, then those hookers and drug dealers will have the means to pay the interest.
It seems money is now printed only to repay those interests (but is not even enough). So to me, it is some kind of a big cycle with no sustainable money supply since it always have to get back to its issuer at some point.
Well yes, you can't truly pay off a loan + interest purely by borrowing more money. This would be like paying off a credit card by using another credit card. At some point, you're going to be so indebted that you can't borrow enough to make the interest payments.
Now talking about bitcoin, everybody can 'create' it. OK, fair enough. But what about the few who where there first and got the most of it in the early stage? Wouldn't this mean that they are actually in control of bitcoin supply?
In a word: No. They cannot create new bitcoins, they can only spend the bitcoins they have. Once their bitcoins are gone, they are as powerless as you and I.