Thus said the Uncreated Light:

Consider, little ones, the Tree-dwellers[^1], the very clay from which I sculpted your form. They move about, seek refuge, nourish themselves, and beget young according to the passions which I have kindled within them. Yet do they gain any merit thereby? By no means! For they do so without understanding. They paint the leaves, yet they cannot write a single glyph[^2]. They call out to one another, yet they cannot chant a single syllable. But to you, little ones, to you alone among the myriads of creatures walking upon the land and swimming beneath the waves and soaring upon the wind of this earth, I have granted the light of understanding[^3]. Now gaze, little ones, upon the countless stars bedewing the heavens. Think ye that I have wrought them for no purpose? Nay, each one shines forth my love. Know ye that there are others like yourselves, in whom I have kindled the fire of understanding. Their bone is not of your bone, their flesh is not of your flesh, yet their souls are like unto your own. search among these stars for other minds, that together ye might meditate upon the mysteries of this dear little creation[^4]. Listen to them for other voices, that they might join you in song. Seek among them other hearts, and offer to them your friendship. Go, dearest little ones, spread your light to the stars, and ye shall become brighter yourselves.

[^1]: A nonsapient species of vulpithecin closely related to the yinrih [^2]: Refers to the yinrih's primordial written language, developed from a scent-marking behavior simultaneously with a spoken language. As such, the yinrih have a written history that stretches back to the dawn of sapience in their species, roughly contemporaneous with the advent of behavioral modernity in humans on Earth. [^3]: "The fire of understanding", or the faculties of language and symbolic thought [^4]: to meditate on the mysteries of Creation, or to undertake scientific research, is regarded as an act of worship, and the accrual of knowledge plays an important role in Claravian eschatology.

The Defenders have our solar system either blockaded or quarantined, depending on who you ask. This prevents extraterrestrial development of Earth, while our own developmental blind spot keeps us from developing our own FTL systems. Individuals can sometimes slip through, but they arrive in force at any hint of large scale fleet movements.

After the first few attempts to reverse engineer alien interstellar drives failed, neuroscientists, parapsychologists, and assorted mentalists began their own investigations. The current consensus is that the concept behind FTL travel is strangely slippery for the human psyche. Common alien concepts like "the folding song", "the scent of the spheres", and "ether stairs" are nonsensical to us, as if we're missing some critical frame of reference. Dr. Adrian Braums in 1968 went so far as to describe this as a "deliberate, species-wide incision", but her subsequent creation of the villain SnapStep has led many to discredit her. Without this crucial insight, we're left with brute-forcing our way out of our gravity well by chemical explosions, and other stars remain out of reach entirely for now.

As for the Defenders, they aren't human. We've always had our own larger than life heroes and villains, gods, demigods, giants, and monsters; but as near as we can tell, the Defenders started paying attention to Earth around 1200-1800 years ago. From records recovered from (non-Defender) alien craft, recollections from alien visitors, and two interviews with Defenders themselves, we know they're an interstellar group of fantastically powerful, insular individuals who typically intervene in planetary scale and larger crises - evacuating planets ahead of supernovas, redirecting rogue black holes from populated systems, etc.

When they first arrived at Earth, they declared it under quarantine, and began intercepting ships attempting to land here. When Yuri Gagarin first made it into orbit, the Defender Oo'Oblansk welcomed him aboard his own vessel; this encounter was only recently declassified, and details remain unavailable beyond it being a "friendly chat". However, vessels from outside our solar system are strongly discouraged, outside of a few rare cases (the Memm refugees being a recent example).

The Defenders have also been implicated in disabling at least one captured FTL vessel that was being outfitted for a human led expedition; they have not revealed their reasons for doing so. However, when interviewed by the BBC in 1984, Oo'Oblansk strongly denied that the Defenders had anything to do with our inability to comprehend FTL travel.

As near as we can tell, there is usually one Defender stationed at Sol system at any given time. They seem to rotate out every decade or so. We've confirmed one other species that the Defenders have blockaded/quarantined in this way; the home planet of the now extinct Krennesek, who also exhibited a wide range of physical abilities and rapid technological progress without interstellar travel. Their planet exploded in 966 CE.