Is it safer for a country to have many different allies or to rely on one very powerful relationship?

Unity is strength

Just like in ordinary life, in politics too it is important to have multiple friends that you can rely on. Therefore I think it's better for a country to have many different allies. If more countries are in an alliance, they can provide mutual protection, backing each other up. For example, NATO has article 5 which states that if someone attacks one country the other countries in NATO treat the attack as an attack on themselves. This acts as a deterrent against potential enemies. For instance Romania worries about Russia but as part of NATO it has an American missile defense system at a military base in the south of the country.

It is not only military alliances that reassure us and make life better, trade alliances are also important. The EU is a good example of this. The EU offers economic security. For example, the EU provided financial assistance to help after Covid.

This being said, there is also a degree of danger if a country is too dependent on others. If you're in an alliance with a more powerful country, they can easily take over your territory and betray you. For example, the USA has repeatedly threatened to take over Greenland and this is a major problem for Denmark.

In conclusion, alliances make countries stronger, provided that they all their members play by the same rules.