E.g.: a country experiences a catatrophic flood and another country sends aid like rations, water or rescue equipment. Is it a 20th century thing?
Hi, you may be interested in a couple of examples from the ancient Mediterranean
When did it become common for civilizations to assist others after catastrophic events? /u/Damasus222 on the 226 BC Rhodes earthquake
Did ancient nations ever send aid to their neighbors or rivals after a natural disaster? - /u/XenophonTheAthenian on the 464 Peloponnese earthquake
Not international aid, but possibly worth noting that domestic aid was an ad hoc affair back then too: a few comments on the 79 AD Vesuvius eruption