I strongly agree that the world today faces problems that require global solidarity and cooperation.
Your quote from Alphonse de Lamartine reminded me of the final words of a hymn from India, the Annapūrṇā Stotra attributed to the sage Śaṅkara: "My homeland is the threefold world."
The nationalist right is one obstacle to what is needed. I'd suggest that another obstacle is the sort of multilateralism which divides the world into rival alliances, cultivating solidarity within each alliance but enmity between alliances.
I'm alarmed by the degree to which this is happening right now; all the more so because it's a temptation that pulls in people on the liberal side of politicals as well as those on the conservative side.