Karma does not relate to any era or timeframe. Karma is equally applicable to a King and a laborer. As our actions accordingly the manifestation! In the field of karma the results do not become available immediately. We just cannot wait for results of our actions!
Karma is deeply ingrained into our psyche. The resultant karma can manifest any given moment of life… now or a few days later, many months or years after, even many manifestations henceforth. This was designed so by god so that intelligent human beings do not manipulate laws of karma. In the field of karma backdoor entry is not possible, nothing could be reversed.
In present Kali Yuga if we find good people suffering and bad people enjoying at times this does not mean karma fails to work. Suppose I presently stood at karmic index of +45 and if I indulge in a bad karma that attracts a negative marking of -3 then the resultant karma would be +42. One would still enjoy life, experience happiness more than sufferings.
Imagine another person who stood at karmic index of +24. Indulgence in good karma resulted in additional marking of +3. The resulting karmic index would be +27, which is far lower than +42. The person at karmic index of +27 would suffer more than one who stood at karmic index of +42. Even though the person with karmic index of +27 indulged in good karma but the resultant karmic index was lower due to bad karma indulged by one in past or previous lives!
In such circumstances none can help but the individual himself. By indulging in good karma, positive karma all the time we can not only neutralize bad effects of negative residual balance of karma from previous manifestations but also improve our present, manifesting destiny forever.
To understand karma in entirety we must indulge in teachings of Lord Krishna in Bhagavad Gita.
In present Kali Yuga (Dark Age) more and more people indulged in bad karma than good karma. Finally the society reaches a point of no return. In that event comes a messiah, savior an avatar (God manifest in human form) to put the society back on its pedestal, re-establish Dharma (righteousness) against all odds.
If in Kali Yuga almost 95% people indulged in bad karma most of time, comparatively in Satyuga (the golden period) 95% people indulged in good karma and only 5% in bad karma.
People remaining the same from Kali Yuga to Satyuga only the indulgence changes. People become more pure in thoughts and deeds in Satyuga.