the other guy is right. though he forgot one tiny thing that makes it the Republic CAN'T be ignored on the "world stage". yes, while defending the giant Tree boosts them and their ships become stronger than the enemy. They also are FILTHY rich, so their technology is top of the line. Only Luxion has better weapons, ships... tech in general.
Now, WHY, are they filthy rich? in the previous manga, it was noticed, certain rocks act as energy sources. The Republic sit on a ridiculous deposit of it. But they don't need it. because the Tree acts as their energy source. So they sell it to the other nations. who can't get it from someplace else... unless they decided to break flying islands. which means give up land to colonize. It's the fucking Arabian Peninsula oil of our world on steroids...
What other nations going to do? not buy from them? okay. you lose a vital energy source while your other enemies keep buying, and suddenly you get left behind in trade, tax, population... your people suffer from prices increasing all the while, the 3rd enemy who keeps buying, gets stronger. The republic doesn't even need to go on the offense, because of how politics work.
but it's fine. it's not like stuff wasn't skipped from the LN to move the plot faster. nuance points get skipped~~