Travel in Periphery

Can someone explain just what could and could not be done with
spaceships and technology available for Empire, early Foundation and
Traders?

In Foundation 2, Salvor Hardin complains that trade ships were not
arriving, that Anacreon was on the last remaining route to Santanni
and Trantor, and that (since it was "last"), other routes had existed
but somehow been cut already. News still travel, though, and Lord
Dorwin travelled to Anacreon and back.

In Foundation 3, Salvor Hardin tells all roads had been cut 30 years
ago, and he did not know whether there was a new Empire or Emperor.
Certainly, no expedition had come from Empire, as would happen with
Bel Riose - but not a single trading ship with news, either. Nor any
kinds of ultrawave broadcasts.

In Foundation 5, we hear that shortly afterwards, many discontented
nobles had emigrated and spread word of Foundation´s perfidy all
around Periphery. Somehow, they got the ships despite disapproval of
priests. A few reached Siwenna.

Given that Anacreon and Smyrna after 80 had abundant ships suitable
for travel in periphery, and in fact already in 50 had warships
capable of a meaningful war between Anacreon and Smyrno, why did they
not use technology and weapons from Foundation to expand across
Periphery by force? For a king of Anacreon or Smyrno, attacking
Terminus meant facing coalition of other 3. Attacking just 1 of the
three could be done, but it would be against an opponent also armed by
Foundation. Whereas attacking remoter states of Periphery should have
been a safe and cheap way to get more manors.

In 154, we see that Hober Mallow could get from Korell to Siwenna in a
few days - 2 days from Korell to leaving in a lifeboat, another 2 days
from Siwenna to meeting his crew again.

If it was so easy, how come no Trader or an official scouting mission
from Foundation had done so before and the continued existence of
Empire was not a common knowledge?

The viceroy of Siwenna, with the technology of 150s Empire, married
his daughter to Commodore and gave them five ships.

How did the warships get through? How did Licia? And how did the
scouts and negotiators for such an enterprise reach Korell?

Especially without the whole Periphery, the Traders and Foundation
knowing?