What is the leading cause of death?

The leading cause of death on Urth varies by the culture of the area. Within cultures that only worship the Primordial Spirits, diseases can become rampant. However, the teachings of some of the celestial gods advance ideas that reduce this.
The god Hospitika teaches how to treat minor wounds, healing, and the need for cleanliness is treating illness. Ghyennie advances the need for waste management in larger towns and cities through the construction of sewers, trash and waste collectors. He also teaches reuse, salvage, and finding value in what we throw away. Potabbarom teaches of the sanctity of water, collecting rainwaters, and understanding the need for clean water.
In areas where these celestials teachings are widespread, war and conflict can become a near constant state under some governance. It is the nature of governance and war, that the leaders that declare war as an inevitability, seldom fight it themselves. And when they do they gather the greatest of their forces to fight around them. They stack the deck in their personal favor. Or they simply never step foot on a battlefield. This makes war an idea, a decision that doesn't require you to plunge a knife into an innocent or toss the corpses of men, women, and children into the pyres. Leaders can make war in a comfortable chair with clean hands. Nations bent on war as the solution can fight wars for years, and even decades. Religious fervor can drive wars for centuries. Such lengthy warring create permanent hatreds of a people, nation, or race. Those hatreds cement into the cultures and will exist for hundreds of years after the arrows stop flying.
Violence is always a factor, and exists outside of the context of war. Urban cities see violence deaths through crime and other creatures feeding on the populace. In the borderlands, where wars over a line on a map are seldom fought, the dangers of living on the borders of civilization may be the greatest cause of death. The myriad creatures of the world, and the underworlds, maintain a constant risk of danger to anyone within or close to the borderlands.
Natural death is a constant, and usually determine by race. A race with an average lifespan of 60, will see 1/60th of their population die each year from age, compared to 1/100th with a lifespan of 100 years. Diseases, malnutrition, filthy living conditions, unclean water can exist in poor regions, even with the knowledge of the gods being present. The poor will always have a higher death rate from avoidable conditions.