I live somewhere (Scotland) where there are no plea bargains. The whole concept seems bizarre to me, essentially negotiating punishment (especially having the prosecution involved in deciding the punishment).
Scotland seems to have negotiated mechanisms that are similar to plea bargaining. It appears that prosecutors can make deals with defendants to replace more serious charges with less serious charges, which carry less jail time, if the defendants agree to plead guilty to those charges. Scotland also appears to give a substantial sentence reduction for defendants who plead guilty early.
"PLEA AND CONFESSION BARGAINING IN SCOTLAND" [1]
"Tensions and balances, costs and rewards: the sentence discount in Scotland" [2]
"Furious 'stalking' victim slams courts for striking plea bargain with man who 'made her life a misery'" [3]
Scotland absolutely has plea bargains, and it's quite prevalent. The distinction with the U.S. system is that the judge is not as involved in the negotiations.[1]
The process of charge and fact bargaining is entirely
dependent on informal negotiations between the
prosecution and the defence. There is no involvement
on the part of the judge. Scotland does not operate
a system of American-style sentence bargaining. This
means that the prosecution cannot guarantee to the
accused that a particular sentence will result if he
pleads guilty (unless the bargain means that the
court’s sentencing powers are reduced because, for
example, the offence to which the accused eventually
pleads guilty has a maximum sentence).
Also, IIUC in Scotland the prosecutor can often impose civil fines and other remedies in lieu of prosecution and do so completely independently of a court. Whereas in the U.S. such arrangements are less often in lieu of prosecution; rather they're terms of an actual conviction and still involve a court formalizing things.
Really it seems the difference between the Scottish and U.S. system is largely semantics, and of course the fact that the criminal justice system in the U.S. is just plain harsh. Our harsher penalties compounded by charge stacking effectively gives courts huge leeway in terms of sentencing. Nobody would agree to plea for a small penalty if a court could unilaterally impose the harshest option. Combined with our constitutional law that all but prohibits a prosecutor from imposing penalties unilaterally (voluntarily or not), and it's clear why our plea bargaining process involves the judge and so-called sentence bargaining more so than in other similar systems.
[1] Or rather, the court gives little or no weight to the terms of the "contract" between the defendant and prosecutor, which can increase the risk for the defendant. Whereas in the U.S. the court has much less discretion to ignore the terms of a plea bargain, and in addition the judge will often mediate, which of course all but guarantees his imprimatur. Therefore there's less risk for a defendant and he will be more likely to take a plea deal.
