Nope. The enemy of your enemy is not necessarily your friend. There are more then two sides. The goals of your enemy's enemy might not align.

My favorite example is when the Polish resistance rose up against their Nazi occupation in Warsaw when the Soviets were closing in. Stalin intentionally halted his advance and let the Nazi's crush the Pols, then the Soviets waltzed in and finished off the Nazis and hunted down the remaining Polsish resistance, knowing they would be tomorrow's enemy.