Historically significant events in Europe between 1404 and 1438

[Mark Knowles]

The princes of eastern and central Europe would vote in a new Holy Roman Emperor.
Eventually it became an elected position.
To become HRE you needed a coalition of alliances and marriages. 

I wonder how this worked in the case of Sigismund, the only person to be Holy Roman Emperor between the years 1404 and 1438, though his reign was only from 1433 to 1437. Why there was no Holy Roman Emperor from 1404 to 1432 I do not really understand. In his case I am not sure how the electoral process worked to make him Holy Roman Emperor.