The US already have a bunch of revived people going, including a Senku-level rationalist and scientist who has discovered the revival fluid in parallel and is in fact much less inclined to be forgiving and wants the exact opposite of Tsukasa, to take advantage of the hard reset to build a full technocracy. By the time Senku & co arrive there, they already have automatic firearms and WW1-era planes. So essentially Tsukasa’s plan was always absolutely doomed. Just like it has happened before, one day backwards isolationist Japan would wake up to find US gunships with superior firepower at its gates and it would be able to do nothing at all to stop them.
Not just that, but as per manga spoilers:
The US already have a bunch of revived people going, including a Senku-level rationalist and scientist who has discovered the revival fluid in parallel and is in fact much less inclined to be forgiving and wants the exact opposite of Tsukasa, to take advantage of the hard reset to build a full technocracy. By the time Senku & co arrive there, they already have automatic firearms and WW1-era planes. So essentially Tsukasa’s plan was always absolutely doomed. Just like it has happened before, one day backwards isolationist Japan would wake up to find US gunships with superior firepower at its gates and it would be able to do nothing at all to stop them.