Religion is not the main cause of war, according to a new report. Instead, war is caused by clashes between different groups, bad government, high levels of corruption and poor relations with neighbouring countries.

Although religion is often cited anecdotally as a root of conflict, little empirical research has been done on the link.

According to a paper by the Tony Blair Foundation on an analysis by the Institute for Economics and Peace, corruption, political terror, gender, economic inequality and political instability are the main causes of conflict. "Statistically speaking religion has only limited explanatory power for outbreaks of violence," the paper says. "The most peaceful countries are not necessarily the least religious, and the least peaceful countries are not necessarily highly religious."

The foundation notes that countries where Sunni and Shia Muslims live side-by-side such as Qatar and Kuwait are relatively peaceful. "The main factors which differ between peaceful coexistence and non-peaceful coexistence relate to well functioning governments, lower levels of corruption and better relations with neighbouring countries," it says.

The institute found that countries with greater religious freedoms are generally more peaceful, whereas countries with less religious freedom are generally less peaceful.

The most influential factor affecting religious freedom is the type of government.

"Full democracies are the most peaceful and have the greatest level of religious freedom, regardless of the type of religious belief or various religious characteristics."

There is no statistically meaningful relationship between the levels of atheism or religious belief in a country and its levels of peace. Four out of the ten countries with the highest levels of atheism are less peaceful than the global average.

The most atheistic countries are New Zealand, along with communist or ex-communist countries.

However, in two-thirds of nations, more than 95 per cent of the population is religious. The economic status of a country make no difference, the report says.

"Of the ten most peaceful countries... only two countries have greater than ten per cent atheists. These countries are New Zealand and Belgium," the Tony Blair Faith Foundation notes. "Of the 15 armed conflicts motivated in part by Islamist groups in 2013, all but five occurred in countries where Muslims were in the majority. Many of the least peaceful countries do not have high levels of religious diversity."