Am I misunderstanding the Wikipedia article?

>There are various ACH systems around the world. The World Bank identified 87 systems in their 2010 Survey

Seems to me like there are many different ACH systems, but perhaps the one referred to colloquially as ACH is specifically FedACH, the American system.

https://en.wikipedia.org/wiki/Automated_clearing_house

ACH is a US-centric term that seems to be used for both the general concept of netted/batched customer-facing interbank transfers, as well as the US-specific set of agreements, rules, participants, and regulating body that together implement one such network.

There are many national and international equivalents, but the linked Wikipedia page gets many of the examples pretty wrong, listing e.g. card acquirers/processors and central banks as examples for other such networks.

Direct equivalents would e.g. be SEPA Credit Transfer (but not SEPA Instant) and SEPA Direct Debit in the Eurozone or FPS (credit push only) in the UK.

> Seems to me like there are many different ACH systems, but perhaps the one referred to colloquially as ACH is specifically FedACH, the American system.

Giro might be the other, possibly broader term for something similar:

https://en.wikipedia.org/wiki/Giro_(banking)

Moreover, not even overseas transfer exists in the "ACH sense". Money is moved between ledgers of the same currency so what you will have is a correspondent bank holding your position in that currency.

There's this.

https://www.nacha.org/content/international-ach-transactions...

It still Nacha which is a US institution as you mention. However, I don't see how that protects in the case of a fraudulent overseas transaction. What recourse do you have if an overseas bad actor tricks you into sending money to his overseas account via international ACH?

I worked for a NACHA processing backend for some years, the mechanism of protecting overseas transactions from bad actors is usually based on sending additional information contained in the IAT transaction, which includes some extra data from both the origination and the receiver[1]. When the bank process it, it could either:

1) settle the transaction in the next few days (3 usually).

2) ask for additional information on the next few days.

3) deny (return) the transaction if it looks too suspicious according to the bank.

[1] https://www.nacha.org/system/files/2019-07/IAT-Specific-Data...