Do international alliances always make the world safer, or can they sometimes lead to more tension?

I think that it depends on if the alliance was made for mutual defence or not. I believe that alliances which are based on mutual defence makes the world a safer place.

One reason for my opinion is, that big defensive alliances discourage stronger countries from attacking weaker countries since the cost fighting multiple countries at once is at most times not worth the things that can be gained from invading a country (e.g. teritory, natural resources). One example for this are the Baltic countries of Estonia, Latvia and Lithuania which are very weak on their own against Russia, whose government said that Russia should restore the old borders of the soviet union. But there has never been an attack on these countries because Russia does not want to fight all the other countries that belong to NATO.

Another reason for my opinion is that members of alliances can share resources. For example, a smaller countries can now achieve larger goals that they could not achive with their own resources. An example for this is the MMF, where multiple NATO countries share their aerial refueling planes to achieve having an aerial refueling plane active at all the times necessary, which most NATO members could not achieve on their own.

My final reason for why I believe that alliances make the world safer Is that alliances promote norms like the rules-based order or the sovereignty of countries. This is more important than ever because some actors are trying to shatter these norms under whose adoption no direct wars between the major powers of the time.

While you could argue against the statement with the argument that international alliances promote arms races (e.g. the nuclear arms race during the Cold War), I do still think that international alliances make the world safer because the arguments which speak for alliances that I listed above overweigh the risk of an arms race.

In conclusion, I agree with the statement that alliances make the world a safer place because they deter agression, share resources and promote norms that secure peace, if enforced.