These tips are derived from the officially documented mechanics of Ebbtide. The game is unreleased and there is no published hands-on guide yet, so treat them as reasoning from the documented design rather than as tested strategy.
This is the single most important point. Resupply runs by truck and helicopter, and routes stretch as the front expands. A heavily defended wall with an open convoy road still collapses - and collapses later, when you are committed elsewhere.
The infected climb walls using each other's bodies as footholds, so a single line is a delay rather than a barrier. Layer high walls with frontline bases and CIWS coverage, and give the climbers something to break on.
Sustained automatic fire against the base of the climbing mass brings it down - the ladder collapses when the bodies under it do. Timing matters more than volume here: fire at the base, not at the top of the wall.
Infected cling to low-hovering helicopters. Keep them flying high, or provide escort suppression for the ones that have to come down low.
Soldiers killed by the horde re-rise as zombies, so a lost position compounds. Pull units back before the body count grows - a fresh position is worth more than a held one full of your own dead.
Combat continues while you are on the tactical map, so the map view is a live information tool rather than a pause screen. Read it to see which flank is about to break, and to redirect orders before the situation is a crisis.
Bird's-eye orders for mass units and repositioning; TAB into an individual soldier, tank or helicopter for the desperate stretch. Constant micro is a losing strategy in a game about a million zombies - micro at the point of contact only.
Rescued survivors are the campaign's force multiplier. Every survivor you leave behind is a soldier you do not have in the next region.
The infected stack and climb, so base layout and wall geometry matter more than raw unit count. A well-shaped position defended by fewer troops beats a badly shaped one defended by many.
The Los Angeles theatre is the tutorial for the World Campaign. The real payoff is the carrier deployment to other regions - and you cannot get there without a survivor force worth moving.