In the early 1900s, Alexander Chizhevsky (sometimes spelled Tchijevsky or various other ways) made very comprehensive investigations in historical processes, especially wars, to try and determine the causes of the processes. He found that existing methods of analysis could not predict major events that were about to happen.
Unfortunately for us in the English speaking world, most of Chizhevsky's writing is in Russian or French and has never been translated into English. Some parts have been, and the investigation into war has been reported in English. Some of this material has also been reported by Raymond Wheeler in America, but I think that Chizhevsky was the originator. It would be good to know the full story on any links between these two.
Chizhevsky first began to observe that conflicts in Russia tended to be cyclic. After publishing several papers on this he expanded his study to world wide conflicts and made an index of battles for the last 2500 years. It showed clearly that there were 9 fairly regular peaks in conflicts each century, or averaging 11.1 years apart. There were other fluctuations, great sweeping rises and falls over longer periods, but this one cycle stood out.
It so happens that the sunspot cycle also has an average period of 11.1 years, so it was natural to begin to look at the connection. He found that the peak in human aggression fairly much coincided with the peak in sunspots. It is natural to wonder as to whether the Sun is somehow causing or contributing to human behaviour.
There are some additional facts available to us now that help to understand this process. I have never seen this fully laid out exactly like this before (excluding things that I have written), but here are a collection of facts that we can connect the dots on:
1. The quantity of different types of radiation vary over the sunspot cycle.
2. There is a continuous stream of radiation of various types, called the "Solar Wind" that arrives at the Earth.
3. Fluctuations in the stream of radiation at the Earth affects the earth's geomagnetic field.
4. There is an oscillation of the Earth's entire electromagnetic field, called the "Schumann Resonance" which oscillates about 7.5 times per second because that is how fast electromagnetic waves travel around the Earth.
5. Bursts of Solar radiation can get the Schumann resonance really ringing. Although the 7.5 Hz mode is the main one, there are also oscillations at near multiples of this: 15, 22.5, 30 Hz and sometimes at lower frequencies such as 3 Hz.
6. Human brain wave frequencies that are commonly studied cover the range from about 0.3 to 40 Hz, and the Schumann resonance is right in the middle of that range. The brain is a largely electrical organ in its functioning.
7. Outside electromagnetic fields can affect the brain by entrainment or in other ways. For example it is known that 10 Hz waves will make human reaction times faster while 3 Hz waves will slow it down.
8. Accidents are more frequent when there are strong ELF or ULF (Extra Low Frequency or Ultra Low Frequency) waves such as 3 Hz. This can be understood as resulting from a slowing down of human reaction times - people are less able to deal with tripping up or sudden events and so more likely to have an accident.
I do not know of evidence that moods are affected by ELF / ULF waves, but would expect that to be the case. Certainly we may say that the evidence is that when the Sun gets uppity, so do people, probably because of electromagnetic waves affecting our brain operation.
My guess is that we all have stored up resentments that we are bottling up, and that when a bit of extra electrical activity is brought to bear on our brains, these then overflow just as they would when the last straw was added by events in our lives. Then all sorts of stuff bursts forth. However when this comes from the whole Earth resonating, it means that many people get agitated at the same time. That is just the recipe for international conflict or social unrest.

For further reading please see:
Chizhevsky's paper (1.4 MB PDF file) as published by the Foundation for the Study of Cycles.
Edward Dewey's War cycle analysis (0.1 MB PDF file). Dewey found other cycles in Chizhevsky,s data also, of which the strongest were 53.5, 23.8, 17.4, 11.2 and 6.0 years.
No Comments for this post yet...
Blog of Ray Tomes research on cycles, news reports on cycles, my original research on the Harmonics Theory and discussion of these matters.
There are cycles in everything. There are cycles in the weather, the economy, the sun, wars, geological formations, atomic vibrations, climate, human moods, the motions of the planets, populations of animals, the occurrence of diseases, the prices of commodities and shares and the large scale structure of the universe. None of these are independent of each other.
Research shows that very different disciplines often find the same cycle periods in their data. The inter-relatedness of all things is an idea who's time has come. The study of cycles is an excellent way to understand this because the periods of cycles are as easy to recognise as fingerprints or DNA sequences.
"The universe, believe it or not, is nothing other than a giant musical instrument with a very special but predictable pattern of harmonically related oscillations which determine the structure of everything from galactic clusters to subatomic particles and we are just parts of the various vibration modes."
The single axiom of the Harmonics Theory is that:
The Universe consists of a standing wave which develops harmonically related standing waves and each of these does the same.