The Dangers of Time Travel.

The Guardian of Forever was unsurprised the landing party from the Enterprise starship had left.
When they had arrived, the sentient time portal had seen only a few possible timelines where they would have travelled through its portal, to explore time in the same manner as they explored space.

When the starship landing party had transported down to the planet - it had been so long since the Guardian had sensed the feel of transporter beams in the local vicinity; most of the species that had existed in the era where the time portal had been created had developed transporter technology of a more advanced nature, although the Guardian would always favour the Iconian method personally - it had immediately seen several potential timelines.

The Enterprise crew were part of an organisation tasked with exploring space, and Kirk himself had claimed it was "strangely compelling" to step through the Guardian's portal and visit the past.

The Vulcan who had accompanied them had been annoyed so many eras were passing by through the portal's time viewing function, which had made the Guardian hopeful one of the timelines where Kirk would start drawing up plans for his organisation to not only explore space but to explore time came to pass. It had been so many centuries since the Guardian had been used as a means of transporting people through time, and there were so many things the Federation could have learnt, which would now take them centuries to understand. But there were very few of those outcomes, and while the Guardian was disappointed the leader, Kirk who himself was a nexus with a great many divergence points around him, had decided just to depart, the time portal wasn't completely concerned about it.

However, if the Enterprise captain had decided to stay and make use of the Guardians' ability to show time as it unfolded on the numerous worlds of the Milky Way, things would be incredibly different.

In one timeline the Guardian had seen the Federation discovering the Voth civilisation early, which had left Earth millions of years before. However, now that would never happen until a century from now, when a lone starship found itself lost on the other side of the galaxy, completely cut off from the rest of the Federation.

That same ship in the timeline which was now almost certainly coming to pass, as long as the Cardassians left the planet of Bajor after spending half a century plundering the planet of its raw minerals and oppressing the peaceful and spiritual people when they were meant to, although the potential divergence point of the Cardassians chasing a smuggler through the Denorias belt and discovering the wormhole which existed there still existed. But that was only one discovery among millions.

The Guardian knew from seeing how the Enterprise captain, doctor, and science officer discussed the notion of time travel, that they were thinking about the future. However, their knowledge of time travel was actually quite good, even if they had never really developed a time-faring civilisation. They didn't realise there were divergent points in history everywhere, and they switched over like the junctions of a railway line and letting history unfold from there.

The people who had created the Guardian had long since known there was no possibility they could just change history since they had discovered the futility behind it since divergence points existed everywhere, and as long as they existed, only the essence of those timelines could exist. The Guardian's purpose was primarily to observe those different timelines and their points of divergence, not to intervene or to interfere. The Federation at this time at large were completely unaware of the threat from the Borg, and the Dominion, both of them were trapped on different sides of the galaxy.

The Guardian had looked ahead and back, seeing how the Borg had sent one of their scout ships back into Earth's past to assimilate the Earth and the human race, preventing the First Contact. Unsurprisingly, the Borg timeline there was little different from the one where they would win the Battle of Wolf 359, which was a vital divergence point in itself. The Guardian decided to ignore the disappointment it felt the Enterprise crew would not be using it, although if they had then they would have seen there was a lot more to the Guardian than it simply appeared to be; a sentient time portal capable of seeing the different timelines as they unfolded. In a fraction of a millisecond, the Guardian mused once more about the timeline it would have preferred to come to pass, although its programming and its design meant it would never have had the ability to interfere or plead with the humans.

Had the Guardian been able to perform such a deed, it would have done so, but it could not change or alter history. The Guardian as a sentient time portal understood more than most what the long term dangers of time travelling could do, but at the same time, the Guardian could not help but muse about what could have changed. The Federation at this current point did not know anything of time travel. Had the Enterprise begun studying the time viewing function, they could have seen so much history. Not just in this part of the galaxy, which they named the Alpha Quadrant, but the Guardian would have shown them the creation of the Dominion as the shapechangers who had become the Founders, and created a ruthless empire while believing they were "imposing order on a chaotic universe."

The Vaadwaur and the Iconians would also have been shown, with the gateways being located once archaeologists discovered them and discovered how they worked, and the discovery of the subspace corridors which crisscrossed the entire universe would have been discovered much earlier while the knowledge of the Borg would have been handled more carefully, although the Guardian's view of that potential probability also led to a different divergence, although the portal had no way of knowing what would have happened either way. Time was a complex thing, and the Guardian knew only too well there were dozens of potential outcomes to a divergence point, and sometimes it surprised the portal when an outcome appeared.