You don't understand modern middle eastern geopolitics. This will work nothing like WW2. More than likely there will be no direct ground invasions from Iran. Just more funding to Hamas and Hezbollah, but if it were to happen, let's look at the countries that we'd have to cross
Iraq is a soulless shell of a puppet state, ever since the American invasion it's been a massive shit show, and a lot of Shia/Sunni infighting. Iranian military can feasibly go through the Shi'a south with nothing to stop them. The Sunni north is extremely unstable and is just waiting for the next isis takeover. No problem.
Syria is another question but to put it simply, it's also such a weak and fragile shell of a state ever since the regime change, and with that, crossing is possible, but a large pain.
Lebanon is an ally because of the Shia hezbollah ruling class, so that's no problem. In conclusion the only half-practical way of getting soldiers there is to fly to Lebanon, but that front is not strategically good, so it won't happen