Nothing below changes today. Both land at the moment the next season starts, so nothing you have in flight right now is affected, and you have the rest of this season to plan around them.
Power decides your place on the leaderboard, and it is built from two things: the levels of your cities, and the size of your army.
Across the top of the ladder today, city levels are about two thirds of all power and armies about one third. That gap is not the real problem though. The real problem is the shape of it: city power grows exponentially with every level, while a troop has always been worth the same flat amount. One high level city is already worth tens of billions of troops, and every level makes the gap wider on its own.
Left alone, that ends in one place. Stacking city levels becomes the only sensible way to rank, and the army you actually fight with barely registers.
A billion troops goes from 2,000,000 power to 3,600,000 power.
That moves armies to roughly half of total power. Cities are not touched: no level is worth less than it is today. Your army is simply worth more.
Less than you would think. We ran it over the live board: the top eight keeps its order bar a single swap, and about half of the top twenty shift by a place or two.
That is on purpose. This is meant to change what is worth building, not to hand somebody else's rank to a player who did nothing differently.
Power also decides the experience you get for attacking someone, through the ratio between their power and yours. That ratio is between the two of you as players, not between two cities: it counts every troop and every city level you both own, so which particular city you hit does not change it.
What does change is who reads as a big target. A player who actually keeps an army now counts for more than one whose power is stacked city levels.
When you attack somebody far below you, the game already limits how many troops you can send and slows the march down. Two of those numbers change:
You can still do it. It stays a legitimate move, and sometimes it is the right one. It simply costs you real time and real attention, instead of being something you set up in a moment and forget about.
Both changes are already queued and will be applied automatically the moment the new season opens. You do not need to do anything, and nothing changes before then.