The most important change has been the one made necessary by the radio and the airplane. Measured in time of transport and communication, the whole globe is now smaller than a small European country was a hundred years ago.
The World is now so small that a major event in any country affects all.
A civil war in Greece or China involves the active intervention of foreign governments, not as arbiters to make peace, but for the defeat of the side whose victory would be against the interest of the intervening power.
An election in Italy is not so much a purely national matter as a local contest between two groups of nations, each afraid of the spread of the political ideologies of the other, and is of almost as much interest in Washington, London, and Moscow as in Rome.
The United Kingdom devalues the pound. Within a few days twenty other nations are forced to devalue their currencies, and all nations to adjust their finance and trade to a decision made by a few men in one country.
We are now physically, politically, and economically one World and nations so interdependent that the absolute national sovereignty of nations is no longer possible.
However difficult it may be to bring it about, some form of World government, with agreed international law and means of enforcing the law, is inevitable.