Islam, like other religions, leaves enough leeway for its different followers to emphasize different aspects. Quran, like OT and NT, even has many contradictions, which asks for different interpretations. Are there sections in Quran that are warmongering? Without any doubt. I'd say Quran can easier be used/abused to justify war and violence, than the NT (and maybe the OT too, not sure about that). But without any doubt, many Muslims don't do that, but rather emphasize the more peaceful aspects.
A long story short: I don't think you can call an entire religion, with all its contradictions, a "religion of war", because this would imply there is just one true way to follow this religion, which obviously is not true. But even if you call Islam a "religion of war", people aren't necessarily warmongers, just because they are Muslims.