You may be right in NATO not defending Ukraine or Taiwan militarily, but economic sanctions would be devastatingly effective. Russia, for all its size, has an economy the size of Spain, and both Russia and China are oligarchies run by the rich who would suffer the loss of their luxurious lifestyles if their income dried up and they were no longer allowed to winter on the Riviera or Costa Del Sol. Even a month's blockade of petroleum income for Russia and consumer goods from China would cripple their economies for months, if not years. We live in interesting times.