Here you have some of our predecessors, promoters of peace or human unity (please, see better primary sources):
Sócrates. Even if he did not write anything, his defense of common sense brought him death. He is not only our predecessor but also he was the inspiration and reference of all cosmopolitans, so were the Cynics as also the Stoics. The best to understand him is the Apology, written by Plato where it is described how common sense, which it is human, universal, is not allowed by the state
Socrates´ followers were the Cynics the first cosmopolitan school in the West, among them: Antisthenes, Diogenes, Crates, Hiparquía…
Zeno of Citium was a disciple of Crates and Hipaquía and the founder of Stoicism, also a cosmopolitan school. It was the main philosophical school in the West from III BC until III AC as much in the Roman Empire area as the Hellenistic area covering up to India. Stoicism very much facilitated the advent of Christianity. The main work of Zeno was The Republic, lost as his other writings, but many other authors refer to it. Plutarch tells us that it could be resumed in a very simple idea, namely that “humans shall not live in the separated system of justice but in the same community” (Plutarch, Live and Fortune of Alexander)
Other Stoics and, therefore, also cosmopolitans were Ciceron, Seneca, Marco Aurelio, etc. They all understood that a human community was impossible in their time, they lived in an unknown world within a sea of nations and religions, therefore they concentrated on understanding the so-called, Logos, or human common sense.
Cervantes shows us with The Quixote that this Logos has to incorporate reality, this determined by the weapons, if it has to be efficient as to be able to set up the human community.
Krause: Author of Humanity Ideal (íd., 1811).
Kang Youwei (1858 – 1927) Author of The Great Union – Datong Shu – 大同書
Sri Aurobindo: (1872 – 1950) Author of The Human Unity Ideal
And many others…