Reference

The Samian standard was replaced by the Attic standard in 412 BC largely due to geopolitical and economic reasons. Samos, an island in the Aegean Sea, was under Athenian influence during this period. The shift to the Attic standard can be attributed to the Athenian desire to standardize currency among its allies and territories to facilitate trade and taxation.

Athens, being a dominant naval power, sought to expand its economic control and simplify monetary transactions across its empire by imposing the Attic standard, which was widely recognized and accepted due to Athens' political and military influence. This move helped Athens to maintain a stronger grip over its allies and to streamline economic activities within the region.

For further reading and verification, you can refer to:

• List of ancient Greek monetary standards on Wikipedia
• Ancient Coinage of Ionia
• Athens and Samos relationship