Internet-of-Things has entered all the fields where data are produced and processed, resulting in a plethora of IoT platforms, typically cloud-based, centralizing data and services management. This has brought to many disjoint IoT silos. Significant efforts have been devoted to integration, recurrently resulting into bigger centralized infrastructures. Such an approach often stumbles upon the reluctance of IoT system owners to loose the dominion over data. We introduce a secured and privacy-safe infrastructure where a federation overlay is distributed among parties and the data control is kept locally. This establishes a league of peers each sovereign of their IoT system and data: League of IoT Sovereignties (LIoTS). LIoTS is scalable by design, allowing iterative formation of domains levels due to the transparency of its federation. Tests show that the overhead is minimal when exchanged data is hefty, and that LIoTS performs better in large IoT deployments than centralized approaches.