International law always sanctioned a state's intervention in another state's affairs. In addition to this very well known fact by jurists, there is also recent works in the field contradicting your position.

"International law prohibits states from intervening in the internal and external affairs of other states [...] as coercion-as-control, an action materially depriving the victim state of its ability to control its sovereign choices. This may be done even through acts like cyber operations that the victim state is entirely unaware of." [1]

[1]: https://www.cambridge.org/core/services/aop-cambridge-core/c...