The Problem:
Typically Buddhists oversimplify karma as: the results of one's actions from previous lives ->
This creates an oversimplified and limited understanding of practice:

Only monks who can fully practice the way of life of the Buddha can extinguish their karma in this life.
Lay followers, especially women, become overly concerned with making ritualistic offerings (dana) to the monks in order to gain merit (punna) towards a beneficial rebirth.

and as: highly deterministic ->
The Buddha:

As the seed, so the fruit.
Whoever does good, receives good.
Whoever does bad receives bad. (Samyutta Nikaya i.227).

Buddhists have generally misunderstood these words to means that any suffering that one experiences now is not due to the exploitation of others or to various social factors. Rather it is solely the fruit of one's actions in a previous life which must be endured with patience, equanimity (upekkha) and a certain amount of resignation.

The Effects of the Problem:
This understanding of karma is disempowering and acts as a form of cultural violence which perpetuates structural and direct violence, such as:

the devaluation of the spiritual potential of women
Birth in female form is often seen as a result of bad karma. This also devalues women in general society. Gender and domestic violence are seen as the consequences of a womanﾕs inferior karma which they must endure with patience.

the legitimization of economic inequality and oppression
The poor and rich are seen as receiving the just results of previous bad karma, regardless of their present moral character or behavior. The practice of generosity (dana) is distorted into a ritualistic system of giving material goods to monks. This system enables the rich to be ﾒbetter Buddhistsﾓ through their ability to make larger and more conspicuous offerings.

the legitimization of oppression political systems
This understanding of karma supports socially passivity in the face of oppression. To resist oppressive power is seen to involve anger and conflict, thereby engendering bad karma. The doctrine of non-violence is distorted as non-action.

An Important Distinction: There is a significant difference between
equanimity (upekkha) towards suffering &
acquiescence with oppression.

Defining Buddhist karma (not other doctrines of karma):

Buddhist karma is "action based on intention (cetana)" or "deeds willfully done" as seen through these simple words of the Buddha:

Monks! intention (cetana), I say, is karma.
Having willed, we create karma, through body, speech and mind.
(Anguttara Nikaya iii.415)

Karma as intentional action creates karma results (vipaka) in the birth (jati) of skillful or unskillful mental states. The accumulation of these mental states express themselves in our mental and emotional conditioning (sankhara). These sankhara serve as the conditions for the creation of further intentional action (karma). This whole process occurs in this very life.

The Buddha said that the determination of how this process works itself out over numerous lives is unfathomable (acinteyya) and is one of the four things that ﾒis not to be conjectured about, that would bring madness and vexation to anyone who conjectured about it" (Anguttara Nikaya iv.77).

Karma is not linear or strictly deterministic, so the actions of a past life do not correspond to exact results in this life. Karma does not mean fortune or the results (vipaka), it just means action. The Buddha said:

Monks, for anyone who says, 'In whatever way a person makes karma, that is how it is experienced,' there is no living of the holy life, there is no opportunity for the right ending of suffering. (Anguttara Nikaya iii.99)

Karma is about choice and choosing wisely for the true benefit of ourselves as well as others (materially, psychologically, & spiritually). Unwise motivations and actions cause suffering; wise, skilful actions alleviate and end suffering.

A Buddhist understanding of Karma empowers us to practice Dhamma personally and collectively. This includes compassionate action towards others in society based on the 4 brahmavihara (friendliness, compassion, joy in others joy and equanimity) and the 4 sangahavatthu (generosity, kind speech, service, equal treatment).

A Path of Intentional Action for Non-violent Justice:

Breaking the silence on patriarchy and gender violence
Deconstructing the cultural violence which imprisons both men and women in harmful structures of gender identity. Learning new types of leadership which are assertive but non-violent and which involve collective power sharing.

Examining the roots of structural economic violence as central causes for the state of misery that the poor experience
Empowering lay Buddhists to develop a practice which supports their daily struggles in this life. Empowering community solidarity by transforming the idea of karma as meritorious ritual offerings (dana) into karma as social service and trust building using the 10 Bases of Meritorious Action (punnakiriya-vatthu). These include rendering service, getting others involved in service, and rejoicing in other's service.

Reconceptualizing the first Buddhist precept of non-harming or non-violence an active term
This means meeting threats to peace and security, at the personal, communal or national level, with methods which are not violent, but directly engage the threat at either the direct, structural or cultural level. In this way, Buddhism is also an active term, not just a system of belief but a path in which the goal, and the method for reaching that goal, are indivisible. Practically this involves, reexamining oneﾕs connections and oneﾕs society's connections with systems of harm and killing and taking measures to remove complicity with them.