Maybe you'd lose against other modern, well integrated forces. But there is a lot of the world whereby forts, trenches, gun emplacements are still their best. And they are simply butter to the modern military knife.
Barring major catastrophe,(ww3, another american civil war, a pandemic that kills large % of younger population etc) it will take far more than 10 years to decline past that point.
The Iraq Military Exercise (I can't call that a war.) is a clear example of that.