DOMContentLoaded event on dynamic content

Question

I am creating a website which prevents normal page reloads on link clicks and instead fetches content and switches the innerHTML of a DIV (kind of a SPA).

I am facing a problem, which I can't seem to able to solve, an example:

If you click on the link "About", I fetch about.php and insert its content into my DIV container (the content is just HTML). Now I will have several php files, some of them contain sliders or galleries etc. where I fire functions like "startSlideShow();" after the event "DOMContentLoaded". As you can guess, the functions won't fire.

I've tried to dispatch the event "DOMContentLoaded" on every route change like this:

window.document.dispatchEvent(new Event("DOMContentLoaded", {
   bubbles: true,
   cancelable: true
}));

But this didn't help. For events like "click" or "change" etc., I can just make use of event delegation by attaching my eventhandlers to my DIV Container...but how do I handle the "DOMContentLoaded" event in this scenario? I am using only vanilla js. -> if anything is not clear, let me know!