6 ideas
Humans are drawn to live in society yet resist it, wanting everything arranged according to their own will and expecting opposition from others. This antagonism of vanity, greed, and lust for power provokes people to overcome laziness and develop their talents, since in an Arcadian life of perfect harmony those capacities would lie dormant forever. Conflict, not concord, is nature's instrument for cultivating reason.
Individual human actions look chaotic, foolish, and malicious, but read at the scale of the whole species they can be treated as if they followed a regular course set by nature. Births, marriages, and deaths seem arbitrary case by case yet show stable patterns in aggregate. In the same way, history can be read as the slow unfolding of humanity's original capacities, even though no individual intends that outcome.
Capacities aimed at the use of reason reach full development only in the species, never in the individual, because each person lives too briefly to learn every use of reason alone. Each generation passes its enlightenment to the next through trial, practice, and instruction. Earlier generations therefore labor for the benefit of later ones who alone will live in the finished structure.
The greatest task for the species is a civil society that administers justice universally, securing maximal freedom for each while limiting it so it can coexist with the freedom of others. It is the hardest problem because humans are animals who need a master, but any master is also a human who needs a master. Nothing straight can be made from the crooked timber of humanity, so only an approximation to this ideal is achievable.
A perfect civil constitution cannot be achieved within one state while states remain in a lawless condition toward each other. The same unsocial sociability that forced individuals into civil society drives states into wars and ruinous arms buildups. Their exhaustion eventually pushes them toward a federation of peoples in which even the smallest state gets its security from united power and lawful decisions rather than its own strength.
Writing history as though it followed a plan toward a cosmopolitan condition is not a replacement for empirical history but a guiding thread that makes the record intelligible. Such a history also has practical force, since believing progress is possible gives rulers and citizens hope and motivation to act toward it. The idea therefore partly helps bring about what it describes.