Some deny the existence of God because war and evil exist, without realising the explanation of this issue goes back to what happened in the Garden of Eden.
All human history and culture results from what happened in the Garden of Eden. There was a lying, deceiving snake in the garden near the tree of the knowledge of good and evil (see Genesis 3). This snake was actually the chief fallen angel or demon called Satan , which in Hebrew means “adversary.” He’s also called the devil, from a parallel Greek term meaning “accuser” or “slanderer” and he appeared as a talking serpent to tempt and deceive Adam and Eve.
The angels were created eons before man and God didn’t force His way of goodness and love on them—nor does He on us. They had to choose to do good and reject evil—which most of them did. However, Lucifer made himself the enemy of God (see Isaiah 14:12-15) by choosing evil rather than God’s way of life, and he led a rebellion consisting of one third of the angels (see Revelation 12:4). Together, they made war on God.
War comes from choosing evil to selfishly and violently get things from others (James 4:1-2) and when Adam and Eve ate from the tree of the knowledge of good and evil instead of the tree of life, which God commanded them to do (see Genesis 2:8-9 and 15-17) they chose that way of life. Thus the way of greed, controversy and war has been the way of mankind ever since.
But what about nations that fight wars to defend themselves or others from attackers? We can understand why some nations have fought “for the right” as they saw it and we can appreciate the service of those who risk their lives to protect their nations. But none of this changes the fact that it was not God’s original desire that human beings would fight and kill one another in warfare.
As a result of Adam and Eve choosing the devil’s way over God’s way their firstborn son Cain started the first human war which is described in Genesis chapter 4. In a jealous rage Cain attacked and murdered his own brother Abel. As the population of the world was so small at this time, the outcome of this action would have been considered a major war.
When Jesus returns to the earth He will stop all human wars, as God originally intended, and establish an incredible era of a totally new, warless human culture. It will be a time when “nation shall not lift up sword against nation, neither shall they learn war anymore” (Isaiah 2:4).
The good news is that you can be part of that peace plan now!