The UK Bribery Act is actually much more severe/punitive that then US version.

The american justice system can judge wether or not they're allowed to continue to operate in america.

The American justice system that hasn't punished Wall Street?

But let's assume American justice system works. But still it seems arbitrary and not clear cut.

If Rolls-Royce is banned from operating in US, does that mean Boeing won't install Rolls-Royce engines on airliners they make for their customers?

Samsung is composed of many subsidiaries that do not look out for each other and it may be that just one or few of the Samsung subsidiaries are involved in bribing. Samsung phone division buys chips from qualcomm instead of Samsung chip division because qualcomm is cheaper (or whatever reason). Will US court ban Samsung from US? Then what happens to the billion dollar chip plant in Austin, Dallas that supplies CPU chips for Apple iDevices?

I don't condone bribing but to me I'm not surprised bribe was needed to get anything done in the nations listed. I'm pretty sure anyone and everyone who has any kind of influence in the said nations require bribe before doing anything. A billion + dollar from US went into Iraq that can't be traced. What's a few hundred thousand or a few million dollars? I highly doubt these companies eagerly bribed people, but they to get anything done in those so called nations, they probably had to bribe.

I was commenting on jurisdiction, not likelihood

More likely the companies will negotiate a settlement without admitting wrongdoing. The US will count it an enforcement success, the guilty parties will escape any punishment, and the loss will be borne by the shareholders, most of whom are investing via investment funds and had little or no idea where their money was going.