Economic factors and a rise in the number of national borders have led to an increase in armed conflicts each year, a new study from the United Kingdom suggests.

The report, which looked at wars that took place between 1870 and 2001, found that the average rise in conflicts is about two per cent annually.

Between 1870 and 1913, the number of annual conflicts between pairs of nations spiked from six to 17.

By the time of the Cold War era, there were 31 annual wars between pairs of states. That number grew to 36 per year in the 1990s.

The study's authors say the data is a counterpoint to a common consensus that the world is a more peaceful place than it once was.

"The number of conflicts has been rising on a stable trend. Because of two world wars, the pattern is obviously disturbed between 1914 and 1945 but remarkably, after 1945 the frequency of wars resumed its upward course on pretty much the same path as before 1913," said co-author Mark Harrison, a researcher from the University of Warwick.

While economic factors like cheaper arms may have led to the increase, Harrison stated that a rise in the number of borders has also led to more conflict.

"More pairs of countries have clashed because there have been more pairs," he said. "This is not reassuring: it shows that there is a close connection between wars and the creation of states and new borders."

Harrison, who is a professor at Warwick's Centre for Competitive Advantage in the Global Economy, said the rise also carries a warning for the future.

"Our planet has already seen two world wars. As that experience suggests, you can never be quite sure what little conflicts will not suddenly snowball into much wider, more deadly struggles," he said in a press release.

Professor Nikolaus Wolf, from Humboldt University, co-authored the study, which was released this week.

The researchers amassed so-called "pairwise conflicts," which include "everything from full-scale shooting wars and uses of military force to displays of force such as sending warships and closing borders."

While the research didn't measure the intensity of the strife or casualties, the data shows the willingness of governments to use force. Civil wars were not included.

A novel aspect of the research is that the "supply" side of wars is often ignored, the researchers said.

While academics generally look at the "demand" side of war -- such as resource shortages or territorial conflict -- the new study offers a different side. Namely, as weapons get cheaper, war becomes more prevalent.

On the surface, the study also appears to identify a paradox: as countries become more democratic and economically wealthy, the number of wars increases.

In fact, the "readiness to embark on military adventures is scattered fairly uniformly across the global income distribution," the study says.

"In other words, the very things that should make politicians less likely to want war -- productivity growth, democracy, and trading opportunities -- have also made war cheaper."