This is how humans could live in a world without war, according to a conflict expert who used to be in the British Army

• Business Insider spoke to Mike Martin, a former British Army Officer and conflict expert.
• Martin's new book Why We Fight is about the evolutionary psychology of warfare.
• He told us about the two reasons that people fight in wars.

Read the full transcript below:

Mike Martin: Hi, my name's Dr. Mike Martin, I'm a former British Army Officer and an expert on conflict, and I've just written a book called Why We Fight, about the evolutionary psychology of warfare. Why is war part of human nature? Well, I think there are a number of reasons for that.

Firstly, and this is the most obvious one, everybody practices warfare. Every society throughout history, almost up to including the current day, practices warfare. Another key reason why war is part of human nature is that humans are part of the animal kingdom and in the animal kingdom, individual animals of every species compete against all the other individuals in that species. And they compete for mates, and for food, and for territory, and for social status.

Humans are just the same, the only difference is that we, as part of the primates, and primates with slightly bigger brains, have got the ability to generate larger social groups. So all that war is is the individual competition that we see throughout the animal kingdom timesed up by our ability to build bigger groups.

So when we're looking at how to free the world of war, particularly when we've argued that it's part of human nature, you have to look right across human history, so you go back 200,000 years and you come right up to the present day.

Now, if you look across human history at that scale, there are two big trends that come out. One is a massive decline of violence.So from the stone age through to the present day, in some cases violence has fallen up to 500-fold. Today is the safest time, without fail, to be alive.

The other macro trend over that period of history is ever-increasing group size. When one group is fighting another in a war, effectively it's the outsides of those groups that are fighting, and the bigger the group the larger the peaceful interior of the group.

So, relatively speaking, the levels of death ie violence, are lower when the groups are bigger, when those groups are fighting a war or having inter-group conflict. But the other reason is this strange statistical relationship that was discovered in the sixties, and that relationship is this: that groups tend to go to war with each other, human groups tend to go to war with each other at the same rate, no matter what the size.

And if groups are part of security structures, like NATO, that counts as a group, but it effectively means that conflict is minimized, 'cause if you have larger groups, you have less groups by definition. Now, these two trends, ever-decreasing violence and ever-increasing group size, correlate.

If we want to rid the world of violence then we need to focus on building the biggest social groups possible. And of course that means a global polity.

Produced by Charlie Floyd.