The process of loading a multiplayer game in Imperialism 1 is full of bugs. There is one process that, if done exactly in order, works as needed and actually loads a previously saved game to resume playing together with others.

First: Backup the saved games or full directories on the host and all peer computers, in case something goes wrong. I consider this the most important step, because if the game gets saved (even automatically) without all players having successfully joined first, they might not be able to join ever again in this save game.
Also, read all steps in full, before you begin and don't do anything that is not stated.

This is how it works (step by step):

H = Host
P = Peer(s)

H: In the multiplayer screen, click on the ship in the bottle to load a saved game. Enter a session name and continue. In the following screen, select the slot that contains the game you want to play.
P: In the multiplayer screen, click the tea set to join a game. In the following direct play window, enter the hosts ip address and click OK. The name of the hosted session will be shown.
H: Click in the "Load" button on the map to load the game. You will be back at the point in the game where you left it. Do not do anything until all peers have successfully joined.
P: Join the shown session. You will be back at the point in the game where you left it. Do not do anything until all peers have successfully joined.

Tags: saved game, savegame, imp 1, imp1, imp I, impI, imperialism 1, imperialism I, imperialismus 1, imperialismus I, gespeichertes spiel, laden, multiplayer, multi player, multi-player