I, too, disagree with this option, to a point. At some time you need to break the alliance with green. In a few turns may be a good time, but first green needs to be in a pitched battle with blue over N.A. and S.A. Let them grind each other down for a few turns. If you allow yellow to get a path towards green to try to invade Africa, then that is your best way of attacking green, i.e. letting yellow and blue do it. Somehow you need to make it more enticing for yellow to do so, and this can be done by attacking in northern asia while keeping the Ukraine more reinforced then the middle east. You also need to keep southern europe fortified to avoid a yellow attack from africa to europe. Enaging yellow is OK, as long as it is not full-blown, but you have the advantage with army bonuses from Europe versus Australia. If green or blue gets the upper hand in their battle, then the time might be right to make an attack on the "winning side" to avoid a powerful foe at your border.
if yellow chooses not to move its way to Africa and instead starts a battle with blue, then green will likely get the upper hand in S.A. and N.A. This means attacking green may come sooner then later. The best move is not to make any rash movements now, you just are not strong enough and all three of your opponents will be significantly strong and looking for a counter-attack on red. The overall goal is to contineu to grow stronger then the other three, and look for opportunities to wipe someone out for their cards if it presents itself.