What kind of international agreements do you mean?Can you explain your question in detail?Or why do they need blockchain in international agreements? its really interesting issue for me...
In general,In most countries which may be the participant of international agreement,there may not be common laws and approaches which prescribe relations based on blockchain as I know,the fact that there are no common approaches it will be very hard to integrate blockchain on international level,But I think you mean: if goverments use blockchain in their public structures? If i guess, its already in use,for example in my country,public service hall uses it for goverment's institutional pursposes and they develop a system for registering land titles using blockchain which is a big success.
As I understand, smartcontracts and blockchain technologies can prevent situations, like had happened in my country. We got rid of nuclear weapon and were guaranteed for inviolability of our boarders. But ... now we see that paper agreements doesnt work. people have short memory, so maybe computers can help)