Unless you were tuning the strings well above the normal pitches for standard tuning (which you say you were not trying to do), this was caused by a defect with the guitar.
Tuning a guitar up to standard pitch should not cause the bridge to come off.
The defect may have been caused by previous attempts to tune the guitar strings too high, which causes greater tension on both the strings and the saddle/bridge.
Or it may have been caused by extreme changes of heat of humidity, which would affect the glue which fixes the bridge to the body.
(I've usually seen this happen when my pupils' guitars have been left next to a radiator for a long period of time.)
It is possible, of course, that you were not tuning the strings to the correct pitches.
A common mistake is to either tune strings to the intended pitch of a different string, or trying to tune up to a note when already sharp, instead of tuning down (in other words tuning in the wrong direction).
If over-tightening the strings is the reason the bridge has come off your guitar, this can be avoided in future through regular tuning; this ensures that strings do not move far from their intended pitch, and so makes it easy to see whether they should be tuned up or down, and so avoids tuning them in the wrong direction or towards the wrong pitch.
music.stackexchange.com/users/9198/Bob Broadley
A possible cause, apart from a faulty gluing of the bridge, is that you were an octave too high.
Seen it happen too often, using a tuner that tells you the target note, but for some reason, you've gone to an octave above.
Thus 4x the tension.
Also seen it happen after it's been left in a place too hot - rad.
, sun, conservatory, etc.
Or, you may have the strings' numbers mixed -
the thin end is E,B,G, the fatter ones are E,A,D, all from the outside.
Seen that before, too...
The solution, even if it's a cheapie, is 2 pack epoxy resin to re-fix the bridge.
It's worked every time for me.
music.stackexchange.com/users/2808/Tim
I'm not sure if it's a manufacturing defect as much as a design flaw.
This should not even be possible for a steel string acoustic.
The ball ends should be held down by the bridge plate underneath the top, not the bridge itself.
See this image: Where did you go wrong?
I'm sorry to say it looks like you'll want to save up a little more for your next guitar to a get a proper design.
music.stackexchange.com/users/6070/Todd Wilcox
Perhaps I have missed this in the other replies but one obvious thing to check would be the gauge of strings you were using.
It's not clear from your question whether you were tuning your current set of strings or you had changed to a new set, but obviously if you were to tune to standard E with a set of strings that were too heavy for how your guitar is set up, the sheer amount of tension could cause the bridge to break like this or the neck to bow.
music.stackexchange.com/users/20154/Stevie
(WARNING: only do this if a guitar has had all the strings taken off for some reason.
For routine string changes, as Tim says below swapping one at a time will reduce flex on the soundboard, and anyway is quicker.)
One tip when stringing in the future is to tighten the strings together.
In other words don't, say, start with all slack strings and tighten the 6th string fully, then the 5th string fully, etc.
Instead bring all of the strings to half tension, then raise the tension in the the centre ones first and work to the outer strings.
The aim of this is to prevent the bridge being "pulled" too heavily from one side.
I've seen this advice for use with classical guitars, but it's probably a good precaution for steel-strung acoustics too.
music.stackexchange.com/users/18664/Andy
I have owned many guitars in my life.
This has happened to me once before.
You did nothing wrong.
The glue joint in your bridge failed.
This is a manufacturing defect.
If your guitar is under warranty, appeal to the manufacturer and get warranty service.
See if they will pay for repairs, or replace the guitar with another one.
Otherwise you are going to have to pay a professional guitar repair technician to re-glue the bridge.
There can be two reasons for this failure.
One is that the bridge was not glued down correctly.
The other is that the neck of the guitar is set at the wrong angle to the body and top, resulting in the bridge having to bear more tension than it is designed to bear, leading to the failure.
music.stackexchange.com/users/None/
I was trying to tune(standard tuning) my acoustic guitar with a digital tuner that captures the playing through a microphone and shows the note/frequency played on its LED screen.   I was completely focused on getting the notes right that I forgot I was increasing the tension in the strings which eventually made the bridge come off.   Where did I go wrong?
Acoustic guitar's bridge had come off while tuning
music.stackexchange.com
<guitar><tuning><acoustic-guitar><bridge>
music.stackexchange.com/questions/32046
music.stackexchange.com/users/8582/whereDragonsDwell
Tuning a guitar up to standard pitch should not cause the bridge to come off. Unless you were tuning the strings well above the normal pitches for standard tuning (which you say you were not trying to do), The bridge coming off was caused by a defect with the guitar. The defect may have been caused by previous attempts to tune the guitar strings too high, which causes greater tension on both the strings and the saddle/bridge. A possible cause, apart from a faulty gluing of the bridge, is that you were an octave too high. It is quite possible that you did nothing wrong in this case. This would seem to be the result of a design flaw or a manufacturing defect. However, it is possible that this was caused by changing the gauge of strings or previous attempts to tune the strings too high.
This would seem to indicate either a design flaw or a manufacturing defect. This could have been caused by previous attempts to tune the strings too high. This could have been caused by changing the gauge of the strings being used. It is quite probably that you did nothing wrong in this case.