"Year" is ambiguous. In the absence of astronomy, it would simply be a cycle of the seasons. However, with astronomy, we have two differing definitions:

1. The year is the interval between equinoxes/solstices. That is, the time from one Spring equinox to the next Spring equinox, or similarly measured by the other equinox or solstices, is one year. This definition gives a year that coincides with the cycle of the seasons. This is the tropical year or solar year, in modern terminology.

2. The year is the period of the Sun's motion relative to the "fixed stars" (i.e., in modern terminology, the stars (excluding the Sun). This gives almost the same year as the previous definition, differing only by the precession of the equinoxes, the 26,000 year-long motion of the equinoxes relative to the fixed stars. This is the sidereal year.

The first year is measured by the Sun's motion relative to the celestial equator, and the second by the motion of the stars. In practice, without precise quantitative astronomy, there is no practical difference between them, unless one uses a star-based calendar for long enough so that the precession of the equinoxes de-synchronises the seasons from the calendar year. This can matter! A number of cultures (at least the Egyptians, Babylonians, and Greeks) used the heliacal rising [1] of various stars to time various seasonal activities, the most famous example being the Egyptian use of the heliacal rising of Sirius to predict the Nile floods. While the 26,000 year precession is slow, it does result in an error of one day for every 70 years - after 700 years, the floods would be 10 days late relative to the prediction. Of course, this doesn't have to be a problem - one simply notes that the heliacal rising of another star corresponds better to the event, and switches to using that.

The old Egyptian calendar year was exactly 365 days, so would desynchronise with the seasons much faster, about 1 day every four years, due to the lack of leap years. This mean that the agricultural year moved relative to the calendar year. The Egyptians were quite aware of this, and we could add the "calendar year" as a third type of year to our list.

This ambiguity was discussed by Ptolemy in his Almagest:

The very first of the theorems concerning the sun is the determination of the length of the year. The ancients were in disagreement and confusion in their pronouncements on this topic, as can be seen from their treatises, especially those of Hipparchus, who was both industrious and a lover of truth. The main cause of the confusion on this topic which even he displayed is the fact that, when one examines the apparent returns to equinox or solstice, one finds that the length of the year exceeds 365 days by less than 1/4 day, but when one examines its return to the fixed stars it is greater.

Ptolemy is one of the few ancient astronomers to discuss this, surely because there is so little difference: the tropical year is approximately 365.242 days, and the sidereal year is 365.256 days, a difference of 20 minutes (as Ptolemy wrote, these are just under and just over 365 1/4 days). Indeed, some ancient astronomers explicitly denied the precession of the equinoxes. However, with precise quantitative astronomy, even with pre-telescopic instruments, this is measurable.

Ptolemy strongly preferred the tropical year, noting that

The only points which we can consider proper starting-points for the sun’s revolution are those defined by the equinoxes and solstices on that circle.

and rejecting the sidereal year:

One might add that it seems unnatural to define the sun’s revolution by its return to the fixed stars, especially since the sphere of the fixed stars is observed to have a regular motion of its own towards the rear with respect to the motion of the heavens. For, this being the case, it would be equally appropriate to say that the length of the solar year is the time it takes the sun to go from one conjunction with Saturn, let us say, (or any other of the planets) to the next. In this way many different 'years' could be generated.

From a modern perspective, contrary to Ptolemy's opinion, it wouldn't be equally appropriate to define a Saturn-year, etc. The sidereal year is, astronomically speaking, the most sensible choice. However, our (modern) calendar year is tied to the tropical year, for the simple reason that the seasons matter more to most people than astronomical logic and simplicity.

[1] The heliacal rising of a star is when it first rises above the horizon before dawn and is visible before the sun rises (and makes it no longer visible). After this first rising, the star rises earlier each night.

You could look at the Julian calendar for that in the west. It would be great to hear from an expert on its formulation and necessity.

What about the adoption of eastern and native/aboriginal calendars?

What were the different ways to pinpoint year 0?