My point: Two tanks can't deal with a trench. 10 tanks can't deal with a trench. They just don't have the right weapons for the job.
What the US Military does, is combine a force of an M1 Abrams + M2 Bradley IFV, maybe with a M109A6 Paladin self-propelled armored Howitzer and a cell-phone that can call an AC-130 if things get really bad.
Each machine is designed for a different situation. For the trench, the M2 Bradley IFV has the ability for anti-trench air burst rounds... and the M109A6 Paladin classic "artillery" can lob explosives at a very high angle and probably hit any trench from miles away.
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M2 Bradley IFV can take a trench: it has grenades, air-burst weapons, machine gun, missiles and more. M2 Bradley IFV has thinner armor however. So the M2 Bradley fighting by itself is still not the best option: if the opponent has a 100mm anti-armor gun in their trench, they may kill the M2.
M1 Abrams can't take the trench, but it can lend its armor to the M2 by driving in front of it: blocking those anti-armor shots and making things safer for the M2. The air-burst attack can likely be done from behind an M1's cover.
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If you know the enemy will only send M2 Bradleys, you simply set up bunkers (covered above-grade concrete structures) with anti-armor cannons. Bradleys only have a 30mm gun, so you can build concrete + steel walls that can stop that attack.
If you know the enemy will only send M1 Abrams, you simply set up trenches (below-grade dug structures). Tanks are direct-fire, and the ground is a surprisingly good shield. The M1 can probably penetrate any reasonably built bunker with ease: thanks to heavy 100mm+ sabot rounds (I forget how big tank guns are but... much bigger than M2 guns)
If you build a trench + bunker, now the opponent has to send the M1 Abrams (for the bunker) + the M2 Bradley (for the trench). Now you have an opportunity for the bunker to shoot the Bradley with a 100mm weapon, killing it. And for the trench to similarly attack the tank, largely with impunity (if the supporting M2 is dealt with).
Or maybe the US Army decides to call in the AC-130 and just pew-pew-pew you from the sky at that point.
Almost all combat is N+1. The holy grail is asymmetric weaponry/tactics. Unfortunately all asymmetric weaponry/tactics is eventually countered through R&D. The critical question is whether one combatant can gain a strategic edge over another during the novelty period of the asymmetric weapon/tactic.
Ah, the joy of the Military Industrial Complex's feature treadmill.
