Throughout human history, many religions have claimed that god was on their side in battles and other struggles. In the Quran, there are very clear claims of divine favor. If this is true, it is hard to see how any god could be keeping his promises.
The Quran is quite explicit in saying that the followers of Islam have divine favor and will therefore triumph, particularly in battle. The following is a prime example of this:
8:65 O Prophet! Exhort the believers to fight. If there be of you twenty steadfast they shall overcome two hundred, and if there be of you a hundred (steadfast) they shall overcome a thousand of those who disbelieve, because they (the disbelievers) are a folk without intelligence.
The problem with intelligence
Starting with the latter party of the verse, its claim that those who do not follow Islam are without intelligence is pretty arrogant and baseless. There is zero evidence that those who follow Islam have a higher intelligence than those who do not. If anything, the backwards state of the Islamic world, which produces almost nothing in the way of scientific inventions, new technology or anything to contribute to human progress, would suggest that those who follow Islam are less intelligent (studies have shown that indoctrination can lower intelligence).
A propensity to violence
Then, there is the overall violent and warlike message of the verse. As anyone familiar with human history knows, people are almost always too quick to fight and not too slow. From the individual level to nations, this has led to many problems in human history. Being aware of this, why would any god stress that people fight in his perfect guidance to them? Looking at the history of Islam and the violence surrounding it to this day, the opposite message, urging people to be peaceful, would have done a lot more good.
Some people argue the intent was only to tell people they could defend themselves. However, if that was the case, why not just speak of self-defense? The author would be a rather poor communicator if that was the intention.
Besides, if Islam is divine word and the creator of the universe wants people to follow it, couldn’t he find a better way to protect it than telling people to fight? It is logical to assume most of Allah’s own creations would flock to Islam is that was his word. Even if that was not so, couldn’t any being with the power to create the universe intervene in some way to keep Islam and Muslims safe? A being with infinite power and wisdom at his disposal should be able to find a better method to spread his word than to have human beings fight for him. Islam should be perfectly peaceful.
Patterns of triumph
Although Islam is supposed to have divine favor, there is no evidence any god is helping it. While Muslims may claim that certain victories were miraculous, nothing has ever happened that could not be explained. If Islam has some kind of divine protection, there would be a clear pattern of victories. Not only do we not see that, but Islam has suffered some of the biggest humiliations.
The most obvious example of this from recent history is the Six Days War. In this war, tiny Israel was able to defeat armies of Muslim nations that vastly outnumbered its own and were equipped with the best weapons oil money could buy, not to mention Soviet aid and advisors. The faithful are supposed to always triumph when outnumbered. As the Jews were outnumbered, did Allah favor the Jews more?
The record speaks for itself
There is no hard evidence of any god ever interfered in any earthly battle. If a god was doing such a thing on the side of any religion, the evidence would be overwhelming and the religion with divine favor would have an undeniable record to prove it. Neither Islam nor any other religion has such a record of battlefield success. Until such a record emerges, claims of divine support in battle should be taken as nothing more than the claims of arrogant or overly hopeful men seeking to motivate their followers.